Professor McGonagall . " Why don't you confer with Mr Finnigan? As I recall, he has a particular proclivity for pyrotechnics. " Seamus . " I can bring it down! " — Professor McGonagall. Neville Longbottom. and Seamus discussing blowing up the Wooden Bridge right before the Battle of Hogwarts [src]
Seamus was a Gryffindor student at Hogwarts School of Witchcraft and Wizardry. He was also the best friend of Dean Thomas. Seamus originally doubted Harry Potter 's claim that Lord Voldemort had returned in 1995. as his mother doubted it, too. However, late in 1995 he eventually joined Dumbledore's Army. an organisation taught and led by Harry Potter, after apologising to Harry. In 1997. he continued his seventh year at Hogwarts, although the school was under the control of Voldemort. Seamus remained in the D. A. in his seventh year and fought bravely in the Battle of Hogwarts.
It can be assumed that he survived the Battle of Hogwarts, since his name wasn't amongst the casualties listed. It is unknown what his life was like after the Second Wizarding War.
Early life (1980-1991)
" [. ] the way Seamus Finnigan told it, he'd spent most of his childhood zooming around the countryside on his broomstick. " —Description [src]
Seamus was born to Mr Finnigan. a Muggle. and his wife. a witch.  at some point between 1 September. 1979 and 31 August. 1980. He had an older cousin, Fergus. who would frequently apparate just to annoy him. Seamus had plans to annoy Fergus back, once he passed his apparition test.
Hogwarts years (1991-1998)
" I'm half and half. Me dad's a Muggle; Mam's a witch. Bit of a nasty shock for him when he found out. " —Seamus regarding his heritage [src]
Seamus in the very front next to Hermione Granger during his Sorting
Seamus arrived at Hogwarts School of Witchcraft and Wizardry on 1 September. 1991. Other students in his year included Harry Potter. Ron Weasley. Hermione Granger. and Draco Malfoy. When Professor McGonagall asked the first years to form a line, to head into the Great Hall. Seamus ended up in front of Harry Potter. When Seamus' name was called during the Sorting ceremony. he waited for almost a minute before the Sorting Hat placed him into Gryffindor. After joining the Gryffindor table, Seamus was introduced to the Gryffindor house ghost Nicholas de Mimsy-Porpington. who students often called "Nearly Headless Nick." Seamus asked how one could be "nearly" headless, to which Nick demonstrated by pulling his head off of his neck, which disgusted most of the table.
During his first Potions lesson the next day, Seamus was partnered with Neville Longbottom to brew a Boil-Cure Potion. Neville managed to melt Seamus' cauldron and was drenched in their potion. Professor Snape told Seamus to take Neville to the hospital wing. which he did.
When the Gryffindor first years learned about their first flying lesson with Madam Hooch. Seamus bragged that, in his youth he spent most of his time flying around the countryside.
Seamus practising the Levitation Charm along with Harry Potter
During Charms class on Hallowe'en morning, Seamus was partnered with Harry to practise the Levitation Charm. While practising, Seamus managed to set fire to their feather with his wand. and Harry had to put it out with his hat. Seamus would have many such experiences throughout his school career.
When Harry was preparing for his first Quidditch match, Seamus joined in to try and get Harry to eat something for breakfast. He insisted Harry needed his strength, because Seekers were the most frequent target of physical attacks. Harry acquiesced, and Seamus piled ketchup onto his sausages. Out in the pitch, Seamus joined Ron, Hermione, Neville, and Dean in the top row of seats. When Harry's broom became enchanted by Quirinus Quirrell. Seamus was impressed (as was the rest of Gryffindor) that Harry managed to stay on the broom.
Before leaving Hogwarts for the Christmas holiday, Seamus lent Harry his Wizard's Chess pieces so Harry could learn how to play. After the new year. Seamus returned for his next term. When Neville arrived in Gryffindor Tower with his legs stuck together. Seamus was among those who burst into laughter.
Before getting on the Hogwarts Express to leave for the summer, Seamus, along with the rest of the school, was given a warning not to use magic. 
" They're starting a Duelling Club. First meeting tonight, I wouldn't mind duelling lessons, they might come in handy one of these days. " —Seamus upon seeing the notice board [src]
On 1 September, Seamus boarded the Hogwarts Express to begin his second year at school. When Harry Potter and Ron Weasley arrived at school via Arthur Weasley 's flying car. Seamus was one of the students who expressed admiration at the result.
Seamus and Neville Longbottom in Gilderoy Lockhart's first DADA lesson
In Gilderoy Lockhart 's first Defence Against the Dark Arts lesson, in which he showed the class a cage of Cornish pixies. Seamus asked if they were dangerous or not. Instead of giving the class a straight answer, Lockhart showed them by letting them loose; most of the class, including Seamus, dove for cover. Seamus was among the students who bolted for the door when the bell rang and escaped the task of putting the pixies back in their cage, leaving the trio to take care of it.
The first and only meeting of the Duelling club that Seamus attended
Seamus later attended the first (and only) meeting of Lockhart's Duelling Club. He was partnered with Ron, and at one point, Ron's damaged wand malfunctioned and knocked Seamus to the ground. Ron helped Seamus to his feet, apologising profusely. When Harry and Draco Malfoy were chosen to demonstrate blocking spells, Seamus and the rest of the class learned that Harry could speak with snakes. 
Seamus . " He's been sighted! He's been sighted! Sirius Black! " Hermione Granger . " Dufftown? That's not far from here. " Neville Longbottom . " Do you think he'd come to Hogwarts? " — Seamus, Hermione. and Neville discussing Sirius Black [src]
A few days before the start of term, Seamus arrived in Diagon Alley to purchase his school books. With Dean Thomas. he saw Harry Potter in Quality Quidditch Supplies. where they were ogling the newly released Firebolt broomstick.
Seamus discussing the appearance of Sirius Black near Hogwarts
In his first Divination lesson with Sybill Trelawney. the class debated whether or not she had seen a Grim in Harry's teacup. Tilting his head from side to side, Seamus expressed his opinion that, tilted right, the tea leaves did resemble a Grim, but tilted left, it looked more like a donkey. In his first Potions lesson, Seamus told Harry and Ron that Sirius Black, an escaped Azkaban convict, had been spotted near the school. Looking excited, he informed them that a Muggle woman had spotted Black and called the special hot line set up by the Ministry of Magic.
After lunch, Seamus had his first Defence Against the Dark Arts lesson with Remus Lupin. When Seamus' turn came to face a Boggart. the creature turned into a banshee with floor-length black hair and a skeletal green face. When the banshee began to shriek, Seamus used the Riddikulus charm to take her voice away; for his participation, Seamus earned five House points.
Professor McGonagall and the residents of Gryffindor Tower in the common room after Sirius Black's break-in
On Hallowe'en, Seamus paid his first visit to Hogsmeade with the rest of the third years. When the Gryffindors learned that Sirius Black had attacked the Fat Lady. they were all sent back to the Great Hall. where they were joined by the other Houses. With the rest of Gryffindor, Seamus was aggravated by the choice of Sir Cadogan to guard the House's portrait hole, calling him a "lunatic". When Seamus complained to Head Boy Percy Weasley. Percy replied that Sir Cadogan was the only one who willingly volunteered.
Gryffindors grouped around Harry Potter's Firebolt
Along with most of the school, Seamus went home for the Christmas holidays. When he returned he was impressed that Harry had received a Firebolt for Christmas. When Harry went down to breakfast the morning of his first Quidditch match with the broom, Seamus served as a "guard of honour" to protect the broom.
When Professor Lupin resigned at the end of the year, after being exposed as a werewolf. Seamus was among the students who were sorry to see him go, along with the other Gryffindor students. 
Bartemius Crouch Jr (as Alastor Mad-Eye Moody) . " You need to know what you're up against! You need to be prepared. You need to find another place to put your chewing gum besides the underside of your desk, Mr Finnigan! " Seamus . " No way. The old codger can see out the back of his head. " Bartemius Crouch Jr (as Alastor Mad-Eye Moody) . " And hear across classrooms! " — Seamus Finnigan and "Mad-Eye" Moody durining a DADA lesson [src]
Seamus in his Yule Ball robes
Over the summer of 1994. Seamus and his mother, along with Dean, attended the Quidditch World Cup between Bulgaria and Ireland. Being Irish, the pair obviously supported the latter; their tent was covered with shamrocks. When Seamus ran into Harry. Ron. and Hermione. they assured him that they would be supporting Ireland, as well. Presumably Seamus was delighted when the Irish National Quidditch team won.
By the start of term, Seamus was still wearing his Ireland rosette; it still called out the names of the Irish players, albeit feebly and exhaustedly. At the Welcoming Feast, Seamus learned that the Triwizard Tournament would be held at Hogwarts that year. Seamus' first day of classes did not sit well with him. In his first class, Herbology. he was required to collect bubotuber pus for Professor Sprout. In his next class, Care of Magical Creatures. he was required to help look after Hagrid's newly bred Blast-Ended Skrewts.
When Harry's name mysteriously came out of the Goblet of Fire. Seamus was among the students who believed Harry had tricked the Goblet into letting him compete. On Christmas Day. Seamus attended the Yule Ball with Lavender Brown. 
Seamus . " Do you believe the rubbish he says about You-Know-Who? " Ron Weasley . " I do. Anyone else with a problem with Harry? " — Seamus arguing with Ron about Harry's claim that Lord Voldemort had returned [src]
Seamus confronts Harry Potter over Voldemort's return
On his first night back at school, Seamus got into an argument with Harry Potter about the latter's claim of Lord Voldemort's return. A devout reader of the Daily Prophet . Seamus's mother believed what the papers were saying about Harry and Albus Dumbledore. and had been very reluctant to allow Seamus to return to school. When Seamus asked Harry what really happened that night, Harry snapped at him to read the Prophet like his mother. When Ron Weasley arrived to break the argument up, Seamus thought that, for believing Harry, Ron was as insane as Harry was.
After Harry's interview with Rita Skeeter appeared in The Quibbler . Seamus apologised for his behaviour. He told Harry that he now believed Voldemort was back and had sent a copy of Harry's interview to his mother. Seamus and Harry were soon friends again.
Seamus' first D. A. meeting where he manages to (for a few seconds) conjure a corporeal Patonus
When the students returned to school after Christmas break, Dean Thomas led Seamus to attend his first meeting of Dumbledore's Army. Seamus was thrilled when he managed to conjure a full Patronus. It disappeared after only a few moments, but was "something hairy." When Dobby the house-elf arrived to warn the group about Dolores Umbridge 's pending arrival, Seamus managed to escape with most of the others.
In the spring of 1996. Seamus sat his O. W.L. exams. 
Seamus at tryouts with his fellow Gryffindors
In the autumn of 1996, Seamus tried out for the Gryffindor Quidditch team as a Chaser. When Katie Bell was sent to St Mungo's after touching a cursed necklace, Seamus was among the students who disapproved of Harry's choice of Dean Thomas as her replacement; Harry was initially against it, as well, because he knew Seamus would not like it. However, Harry felt it was the right choice, because Dean had outflown Seamus during the try-outs.
When the sixth years learned about Apparition lessons in the spring of 1997, Seamus was among the group of students who were impressed that Harry Potter had already experienced it through Side-Along Apparation with Albus Dumbledore.
The funeral of Albus Dumbledore that Seamus attended
Seamus was not one of the Dumbledore's Army members that answered the call to arms when Hogwarts was invaded by Death Eaters. as he did not keep his DA coin on himself at all times. After Dumbledore was killed by Professor Snape. Seamus refused to return until after the funeral wanting to pay his respects and say goodbye to his former headmaster, despite his mother insisting he returned home at once. 
Seventh year and Battle of Hogwarts
" Harry cast more Shield Charms, and Voldemort's would-be victims, Seamus Finnigan and Hannah Abbott, darted past him into the Great Hall, where they joined the fight already flourishing inside it. " —Description of the second half of the Battle of Hogwarts [src]
D. A. members welcome Harry back to Hogwarts
While Harry. Ron. and Hermione were gone searching for Voldemort 's Horcruxes. Seamus returned to the Death Eater - controlled Hogwarts for his seventh year. He greatly missed his best friend Dean Thomas. who was forced to go on the run because of his presumed Muggle-born status. Seamus was part of the restored Dumbledore's Army who ended up staying in the Room of Requirement to escape the Carrows. He, along with many others, showed the cost of standing up to the new regime at Hogwarts: his face was so bruised that when Harry returned to the school in May of 1998. Seamus was unrecognisable until he spoke. 
When Voldemort's army attacked the castle, Seamus was among many of those who stayed to fight. During the Battle of Hogwarts, Seamus, along with Luna Lovegood and Ernie Macmillan. saved Harry, Ron, and Hermione from hundreds of Dementors by casting the Patronus to hold them back, before Harry drove them away with his own. His Patronus was in the form of a fox.
Dean, Seamus, and Aberforth after the battle
Seamus was among the students to witness Hagrid carry Harry's "dead" body back to the school grounds, when Neville shouted "Dumbledore's Army," Seamus was among those in the crowd that roared with cheers, provoking Voldemort. Afterward, when the second stage of the fighting began, and Lord Voldemort himself had stepped in, Harry saved Seamus and Hannah Abbott 's lives when Voldemort had sent a curse their way. Seamus also witnessed Harry Potter's final defeat of Lord Voldemort and the end of the Second Wizarding War.
Later life (post 1998)
He survived the Second Wizarding War and was seen sitting with Dean Thomas and Aberforth Dumbledore once the battle had ended. It is unknown what happened to him after the war. It can be assumed that he attended the 2014 reunion of Dumbledore's Army.
Being a Gryffindor, Seamus usually wore a red-and-gold tie and a black jumper along with his black Hogwarts robes. His uniform was always scruffy and untidy, making him look like a slob. During Seamus's final year at Hogwarts, his face had been battered and bruised by the Carrows to an extent that neither Harry nor Dean Thomas could recognise him, until he spoke with his distinct Irish accent. Seamus had sandy coloured hair.
Personality and traits
Seamus accidentally sets his goblet on fire
Through his school years, Seamus generally appeared good-natured and easy-going. He was also rather clumsy, as he set fire to a feather he was supposed to be levitating in his first year. As suggested by his name, Seamus comes from an Irish family as shown in the Quidditch World Cup he attended just before his fourth year. He seems to display traits of more than one Hogwarts house, since the Sorting Hat had to think for almost a minute before deciding to sort him into Gryffindor.  Seamus is also very curious, asking Professor Quirrell where he got his turban. Nicholas de Mimsy-Porpington how he could be "nearly headless" and Professor Snape about Inferi.
Of all the boys in Harry's dormitory, Seamus was the least enthusiastic supporter of Harry Potter and Albus Dumbledore. often demonstrating scepticism of Harry's claims. However, after reading Rita Skeeter's interview with Harry in the fifth year, he apologised to Harry and sent a copy to his "mam", as she did not believe that Voldemort was back. He did join Dumbledore's Army sometime in 1996. although he did not sign the actual membership list of the group.  After Dumbledore's death the following year. Seamus insisted on remaining at Hogwarts in order to attend the funeral for the fallen headmaster, despite his mother's wish to remove him immediately from the perceived dangers at the school, demonstrating his allegiance to Dumbledore and Harry. 
Seamus also demonstrated the characteristic bravery and loyalty of his house by opposing the Death Eaters at great personal risk during his final year at Hogwarts and in the final battle. 
Magical abilities and skills
Seamus Finnigan's Patronus during a D. A. meeting
Charms . Seamus achieved a high O. W.L. score in this subject, which enabled him to attend the N. E.W. T.-level class. In 1996. during a Charms lesson, he was able to cast the Water-Making Spell. During the Battle of Hogwarts, Seamus was able to effectively cast the highly advanced During the Battle of Hogwarts Seamus was able to cast the highly advanced Patronus Charm - his corporeal Patronus took the form of a fox. 
Duelling : As proven by his participation in and surviving the Battle of Hogwarts, Seamus was a skilled duellist. He and Hannah Abbot were described as "joining the fight already flourishing inside it' during the battle.
Pyrotechnics . Whilst not a specific branch of magic, Seamus is very skilled in his ability to conjure or create magic that will have a pyrotechnic effect. This was demonstrated usefully during the Battle of Hogwarts when Professor McGonagall instructed Neville Longbottom and Cho Chang with the help of Seamus to explode the bridge in the Hogwarts grounds.
Transfiguration : Seamus achieved a high mark on his O. W.L. exam, proving his proficiency in the subject. He advanced to N. E.W. T. - level.
Defence Against the Dark Arts : Seamus achieved a high O. W.L. score in this subject because of his association with Dumbledore's Army. He advanced to the N. E.W. T. class in 1996. 
Wand . Like all wizards and witches it can be assumed that Seamus's wand was among his most valued possessions and that he purchased it from Ollivanders at the age of eleven. His wand was of unknown length, wood, and core material.
Harry Potter . " And your mum believes them? " Seamus . " Well, no one was there the night Cedric died. " Harry Potter . " Oh, well I guess you should read the Prophet then, like your stupid mother. It'll tell you everything you need to know. " Seamus . " Don't you dare talk about my mother like that! " — Seamus and Harry row in 1995 [src]
Seamus appears to have a very close relationship with his family, particularly his mother. They attended the 1994 Quidditch World Cup together . and one of Seamus's main reasons for doubting Harry Potter 's story that Voldemort had returned was his mother's belief in the Daily Prophet 's version of events . However, Seamus felt strongly enough about attending Albus Dumbledore 's funeral to defy his mother's wishes that he return home immediately .
Seamus's best friend was Dean Thomas. one of his dormmates, during their first year at Hogwarts, and the two remained best friends throughout their school years. The two were often seen together at school, and Dean attended the Quidditch World Cup with Seamus and his mother in 1994. Seamus initially believed the smear campaign the Ministry of Magic and the Daily Prophet ran against Harry Potter when he claimed that Voldemort had returned, but this does not appear to have affected his friendship with Dean, who did believe Harry and who eventually managed to get Seamus to attend the final D. A. meeting of the year.
Seamus was also displeased when Dean was chosen as the replacement Chaser for the Gryffindor Quidditch team over him when Katie Bell was injured, but again, the two still remained close friends. Since Dean could not  return to Hogwarts for his final year, the two did not see each other for some time. When Dean eventually did return to Hogwarts in 1998 to fight in the final battle, Seamus was ecstatic to see him, and ran to hug him.
Seamus is also friends with his other roommates, Harry Potter. Ron Weasley. and Neville Longbottom. though not to the same extent as with Dean Thomas. He and Harry had small fallings out over Harry being chosen as a Triwizard Champion  and Seamus's doubt over Harry's claim that Lord Voldemort had returned . but managed to patch things up. When Ron had a row with Harry himself about the Goblet of Fire choosing Harry as a champion, he spent a lot of time with Seamus and Dean. However, when Seamus expressed his disbelief about Harry's statements that Lord Voldemort was back, Ron supported Harry and got very angry with Seamus. However, they became friends again. Seamus was also a friend of Hermione Granger. Lavender Brown and Parvati Patil who were also Gryffindors in his year.
Seamus also seems to have been friendly with classmates and fellow D. A. members Hannah Abbott. Ernie Macmillan and Susan Bones ; during the Battle of Hogwarts. he was frequently seen fighting alongside them, even though his best friend Dean Thomas had returned to Hogwarts. His friendships with Hannah, Susan and Ernie may have became closer when Dean was on the run and he had to make new friends, both Harry and Ron were also absent from school leaving Seamus with only Neville as a friend.  Seamus had also met other members of the army, such as Ginny Weasley. Angelina Johnson. Alicia Spinnet. Lee Jordan. Fred and George Weasley. Colin and Dennis Creevey. Michael Corner. Anthony Goldstein. Terry Boot. Luna Lovegood. Cho Chang. Marietta Edgecombe. Justin Finch-Fletchley. and Zacharias Smith. although their relationship with Seamus is unknown.
Harry Potter and the Order of the Phoenix - Fighting with Seamus