Finnegan is proud to serve as a summoner to the mysterious Phantom Society. A former boxer, his COMP uses brass knuckles-type weapons. One of the organization's top summoners, he has frequent encounters with the protagonist. Self-confident and skilled, he is popular but has many enemies.
He is first encountered during Urabe Kouichirou's Vision Quest (where the protagonist sees Urabe's final moments). He finds Urabe in the computer room, where Urabe downloaded Nemissa to his GUMP (after deleting the Devil Summoning Program), and mocks him. Urabe attempts to escape, but is eventually cornered and killed by Finnegan's gunshot.
He appears at the beginning of the second Vision Quest where Nishi had given orders to Judah to deal with the demon at the airport. Finnegan is later sent there after Judah's failure and kills Winpe permanently, disappointed by how weak Judah was to get killed by the demon. After meeting the protagonist and Nemissa, who blurts out that they know the Society's plans, he sics a Yato no Kami, La Llorona, Jueyuan, and Bai Suzhen on them. He leaves afterwards, believing his demons will finish them off.
Realizing that they beat his demons, Finnegan posts a challenge to them on Summoner Net. He takes Yu-ichi captive when he attempts to challenge him in their place. After meeting Finnegan in Amami Float he states he will not hand over Yu-ichi until he is defeated and that this fight had nothing to do with the Phantom Society. His true purpose being to heal his wounded pride. He gives the protagonist the choice of fighting one-on-one or alongside Nemissa. He heals the party if Nemissa doesn't battle. He summons the demons you currently have out (he can't summon Zeed) in the same formation as your demons for the battle itself. Surprised and exhausted after his defeat, he tells the protagonist he has yet to taste his full power before leaving.
Later, the party encounters him again after the Algon HQ has been overtaken by a Demon and a seal has been placed over the building. (Nemissa can access it by cyber-diving through Paradigm X then to Algon) Finnegan allows the player to listen to him - if so, he explains that six seals have to be unlocked in order to be able to fight the demon causing the situation. If the player refuses either to listen or co-operate, they will engage in battle with Finnegan, and if victorious, Finnegan will die. However, if they co-operate, they are given another choice - red or blue seals. Upon unlocking their seals, the player will reunite with a bloody and beaten Finnegan outside the demon's room, where he informs the player that the demon can silence magic from demons and he was useless without it. Upon dying, he laments the fact that Urabe stole Nemissa from them and tells the protagonist that he will meet the same fate someday. Nemissa tries to ask him for information, but is too late.
After the demon is defeated and the party returns to HQ, Yuichi relays a message that the rest of the Spookies were kidnapped and taken to Amami Monolith. Rei Reiho clarifies that Yuichi, after Finnegan's abduction of him at Amami Float, was brainwashed by Finnegan.