When his brother is permanently brain-damaged in a fight with a rival at a funeral, Ryan, blaming himself, goes on a drug-and-alcohol-fueled rampage throughout the city.
In the second season, O'Reily is enjoying his new status in the Oz drug scene when he is diagnosed with breast cancer.
O'Reily then admits his guilt in Preston Nathan's murder so that he can remain in Oz to protect Cyril.
Furious, O'Reily joins forces with Tobias Beecher and Chris Keller, two other inmates who are looking to get even with Schillinger.
Because Andrew has been trained as a member of the Aryan Brotherhood, he can't bring himself to buy drugs from those inmates.
After Andrew (having befriended and received counseling from Beecher and becoming clean from drugs) publicly embarrasses his father, Vern Schillinger, by ignoring his attempts to reconcile with him and renounces his racist beliefs, his humiliated father gives his son enough heroin to overdose when Andrew is sent to the hole as a kind of test – which he "fails" by dying.
Murphy and O'Reily bond over the Spanish Armada myth of the Black Irish and develop a kind of friendship.
Alvarez loses, the Latinos look worse, and Carmen Guerra grows suspicious of O'Reily's winning streak.
O'Reily arranges the death of William Cudney, who threatened to expose him for cheating, and spikes Pancamo's water with heroin.
O'Reily and Cyril participate in an interaction session with Gloria Nathan and her deceased husband's parents.
A woman named Suzanne Fitzgerald (played by Betty Buckley) comes to visit, claiming to be his birth mother.
Meanwhile, Provisional IRA member Padraig Connolly arrives and plans with O'Reily to blow up Em City.
At the last minute, O'Reily decides that it is wrong and that many people including his brother and Dr. Nathan may be harmed, but Connolly attempts to set off the bomb early.
O'Reily's mother turns herself in and Governor James Devlin reduces her charge to a two-year community service sentence at Oz.
Inmate Li Chen arrives shortly afterward, and Jia Kenmin plots with him to put the O'Reily brothers on death row.
O'Reily, in the meantime, shares a cell with Father Daniel Meehan, an Irish-American priest imprisoned for his part in a violent protest, who helped prison psychiatrist Sister Peter Marie Raimondo fight for Cyril's life.
He convinces officer Robinson that Kenmin talked badly of the guards and, as a result, they kill him in the solitary confinement ward.
With Meehan's guidance, O'Reily opens up about his childhood traumas and, after a while, finally joins the effort to save Cyril.
O'Reily forces Shupe to tell the truth to Cyril's attorney Arnold Zelman, who is unable to get him to testify.
Ryan O'Reily is last seen wheeling Seamus onto a bus during an attack involving a mysterious contaminate orchestrated by Keller.
20 years ago after the evacuation of Oz, the police officer who testified at O'Reily's trial is charged with shooting a minor and turns out to have a long history of corruption, so all his cases were thrown out and Ryan was subsequently released, meaning there will be no retrial.
Sean O'Sullivan and David Wilson describe the character as "the arch schemer,"[1] while USA Today labels him as "Oz's resident troublemaker".