Parker is named after the famous fictional conman Parker, created by Donald E. Westlake under the pen name Richard Stark. Just as in the novels, Parker is only ever referred to as "Parker". No first (or possibly last) name is ever given, though both the Leverage character and the one from the novels is known by many aliases.
There are multiple references to Doctor Who through the whole series. Nathan Ford's aliases are all names of actors who portrayed The Doctor. Additionally, Harrison wears a bow tie during Season 5, and when questioned, says "Bow ties are cool." During The Frame Up Job Sophie and Nathan introduce themselves as agents Tennant and Smith.
Though seasons 2 through 4 were set in Boston, filming was actually done in Portland, Oregon. In The Three Strikes Job when Eliot is impersonating a baseball player he makes a reference to having played in Portland. Moreover, the ballpark they are stealing, PGE Park, and the Beavers are in fact Portland's baseball team. In season five, the Leverage team finally makes their move to Portland in the show as they film there anyway.
Both Aldis Hodge and Christian Kane played roles in versions of Friday Night Lights. Christian Kane played Brian in the movie, while Aldis had a small role in the TV series for six episodes as Ray "Voodoo" Tatum.
In "The 10 li'l Grifters Job", Nate (Timothy Hutton) dresses up as Ellery Queen, and says he was "the world's greatest detective". Timothy Hutton's real-life father, the late actor Jim Hutton, played the titular character in the "who done it" show Ellery Queen.
While the Parker in Leverage is a tribute to the Donald Westlake character, somewhat more faithful versions of Parker have been played by Lee Marvin (Walker in Point Blank), Mel Gibson (Porter in Payback) and Jason Statham (Parker in Parker), among others.
Richard Chamberlain is in two episodes as the character Archie Leach. That is also the name of the character played by John Cleese in "A Fish Called Wanda." Cary Grant's birth name was Archibald Alexander Leach.
Kari Matchett, who plays Nate's ex-wife in several episodes, Saul Rubinek, who played Victor Dubenich in The Nigerian Job and The Last Dam Job, and James Tolkan (The Cross My Heart Job) also had roles in the TV series A Nero Wolfe Mystery (2000), for which Timothy Hutton was an executive producer and in which he was a co-star. Kari played the girlfriend (Lily Rowan) of Timothy Hutton's character Archie Goodwin, along with some other roles in this repertory-company type series. James Tolkan was also part of this company and appeared in many episodes. Saul had a recurring role (as Lon Cohen), and also appeared with Hutton in the TV movie The Golden Spiders: A Nero Wolfe Mystery (2000) (as Saul Panzer).