|First appearance||"Out o' Time" (episode 3.08)|
|Last appearance||"Exeunt Omnes" (episode 6.08)|
|Reason/Cause||End of Series|
|Date of Conviction||February 3, 2003|
|Spouse|| Tessie O'Reily (Wife, deceased)|
Suzanne Fitzgerald (Ex-Girlfriend)
|Relatives|| Ryan O'Reily (Son)|
Cyril O'Reily (Son, deceased)
Brenda O'Reily (Sister)
Shannon O'Reily (Daughter in-law)
Carolyn O'Reily (Daughter, deceased)
|Episode Count||6 Episodes|
|Portrayed by||Kevin Conway|
- "I don't give a shit about anything I can't control."
- ―Seamus O'Reily[src]
He is the father of inmates Ryan and Cyril O'Reily. Seamus is an alcoholic who abused his sons physically and emotionally when they were growing up. He is later convicted of murder and sentenced to Oz during its final season. He is deeply resentful of his sons as he believes that he provided a good life for them and they destroyed it. Although initially unsympathetic and cruel, Seamus becomes more sympathetic as he expresses deep regret on his own life and wishes he could have done better for his own sons.
Seamus is first seen at Season 3, during the Boxing Matches between inmates. Ryan calls Seamus to an "urgent visit". When he discovers that Cyril is boxing, Seamus starts mocking him. When Cyril asks him to stop, Seamus slaps him. During the fight between Cyril and Muslim leader Hamid Khan, Ryan orders Cyril to imagine that Khan is Seamus. Cyril flies into a rage and knocks Khan out, causing cerebral damage that puts Khan into a coma.
Season 4, Part IIEdit
Seamus visits Ryan and confirms that Suzanne Fitzgerald is indeed Ryan's mother.
In Season 5, it is revealed that Ryan and Cyril are only half brothers and Ryan meets his biological mother, Suzanne Fitzgerald, who also grows close to Cyril, despite having no relationship to him. It is also revealed that Ryan had a sister, and as a child witnessed Seamus shaking her to death. Following Father Daniel Meehan's advice, Ryan finally confronts his father about this and vows to kill him if he ever leaves Oz. It is suggested that Seamus impregnated Cyril's mother Tessie the day Ryan was born as he claims in a dispute with Susanne that he had sex with Tessie on the day Ryan was born.
In Season 6, Seamus himself is arrested and comes to Oz. Jealous about the relationship between inmate Jahfree Neema and his ex-girlfriend Suzanne Fitzgerald, Seamus asks Aryan leader Vernon Schillinger to kill Neema. Schillinger declines, and Seamus tries to do it himself. In the delivery room, Seamus tries to stab Neema, but he is stabbed instead. In the hospital, Seamus refuses to see Cyril before his execution. After getting a speech from Suzanne about how he destroyed both his sons' lives and how no one will care about him when he dies, he decides he finally wants to see Cyril, Ryan tells him it's too late, and Cyril has been executed. Seamus begs his living son for forgiveness which, surprisingly, he receives.
Season 4, Part II
- Carolyn O'Reily: Shook her to death to make her stop crying.
- His Co-Worker: Ordered his other co-worker to crush him with a car. (2003)