He was portrayed by Martin Sheen.
Before the SIU
Queenan grew up in Boston, although he didn't live with his father. At a certain point in his life, he became Captain in the Boston Special Investigation Unit. He married and had his son Patrick, who studies at Notre Dame.
Billy Costigan recruitment
In 2006, Queenan met Colin Sullivan, who was beginning his work as a sergeant in the SIU, and later met Billy Costigan, who wanted to become a state trooper, but given his involvement with the Irish mob by father, along with Dignam will give him a job as an undercover agent, which was to infiltrate Costello crime family.
The meeting at the 344 Wash
After a constant work on the case of Costello, Costello and his organization discover that there really is a "mouse" in Costello's organization. Feeling more and more petrified, Costigan plans a meeting with Queenan at 344 Wash down K street. After arriving, Costigan discovers that Queenan has been stalked, not only by Sullivan's men, but also by Costello. Queenan tells Costigan to leave, saying he can't protect him with him here. Being surrounded by Costello's men, Queenan is captured by them, led to the roof and then thrown away. It is not known if Queenan had died before being knocked off the roof, since he did not make any sound help, but it is claimed that the fall is what killed him.
- Originally Gerard McSorley was cast as Oliver Queenan, but had to drop out of the project.
- Robert De Niro was considered for the role of Queenan.
- Martin Sheen was one of the last actors cast. The reason why he agreed to appear in the film was because he wanted to work with Martin Scorsese.
- Oliver Queenan is based on Thomas B. Duffy, a retired Massachusetts State Police Major, who worked out of Boston for nearly thirty years, and specialized in organized crime. He was particularly involved in the case against notorious South Boston mob boss James "Whitey" Bulger, on whom Frank Costello is partly based. Duffy appears as the Governor, who delivers a speech to the graduating police cadets.
- He is inspired off of Superintendent Wong Chi-Shing from Infernal Affairs (2002).
- When Billy is at Queenan's house, sitting on the bench with photo frames and pictures on the wall behind him, a frame depicting "the Last Supper" appears and disappears when shown from different angles.
- In one scene, Queenan hands Costigan a glass of ice water, which disappears and reappears between shots.
- Captain Queenan mentions to Billy Costigan that his son attends Notre Dame. Martin Sheen's character from The West Wing (1999), President Josiah Bartlet, went to the same university, and was also a fan of the Boston Celtics.
- In the subway scenes Queenan and Costigan enter car #01844, and exit car #01884.
- When Queenan and Costigan are riding the Red Line, Queenan gets on at Park Street. Costigan tells him, "Get off at the next stop, South Station." South Station is two stops away; the next stop after Park Street is Downtown Crossing. Queenan gets off at the next stop, and the signs say South Station.
- After Queenan is thrown from the roof, the next shot is from Costigan's point of view. When Costigan moves his head slightly to the right, the dolly track appears briefly.
- When Queenan's body is coming down from being thrown from the roof, Costigan looks up before Queenan's body is in plain sight.
- When Queenan is thrown off 344 Washington St., a lot of bright red blood is splattered upward, then his body hits the ground. A shot of Queenan's body on the grounds shows a little dark red blood.
- His name may be a reference to the comic book character Oliver Queen.
- The murder of Myles Kennefick takes place on September 19, 2006, making The Departed set in 2006. At one point in the film, during a meeting with Queenan and Dignam, Billy Costigan mentions that a year has passed, coming to 2007. In the Colin phone "Mar 16,06", or March 16, 2007 (2006, it is a plot error, as Kennefick died in September of this year). On this day the affair between the Chinese mob and Costello takes place. They pass six months, expressed by Billy, four from the Chinese deal. The events that follow take place day after day, and Oliver Queenan's death takes place five days after the deal (16), making it July 24, 2007.