Roberts was born in Queens, New York to parents Don and Penny Roberts, but spent the majority of his childhood in Secaucus, New Jersey, where he moved at age four. Roberts is a 1987 graduate of Grinnell College in Iowa, where he majored in acting. After graduating college, Roberts moved to Milwaukee and eventually to Chicago where he became involved in improvisational comedy, studying improv under comedy legend Del Close.

In the early 1990s, Roberts and Matt Besser (along with several other Chicago improv comics) would eventually form the Upright Citizens Brigade sketch comedy troupe, Amy Poehler and Matt Walsh would later join the group, forming the UCB foursome who went on to create their own Comedy Central series and later opened the affiliated Upright Citizens Brigade Theatre in New York and Los Angeles. Both theaters have become well-known hotspots for watching live alternative comedy and improv shows and in recent years have helped launch the careers of many of today's most popular comedians.

Roberts wrote and starred in the limited release film Martin & Orloff, and appeared with memorable supporting roles in films such as The Legend of Ron Burgundy, Bring It On, The Ballad of Ricky Bobby, Drillbit Taylor, Miami and Semi-Pro. On the Upright Citizens Brigade's sketch series on Comedy Central, Roberts was often seen as the UCB Agent Antoine, but also portrayed many other sketch characters such as Steve Youngblood and Astronaut Mike Birchwood. A running joke on the sketch series was that his character (Agent Antoine) was thought by the other UCB Agents (Colby, Trotter, Adair) to be a cyborg despite his constant assertions to the contrary.

Roberts, along with his other UCB castmates, has regularly appeared in sketch comedy segments on Late Night with Conan O'Brien for many years. Roberts also had a recurring character in the sitcom Arrested Development, Dr. Fishman (AKA The Literal Doctor, AKA Dr. Wordsmith).

Roberts was one of the new additions to the cast of Reno 911! in its final season, playing the role of Sergeant Jack Declan. Roberts is currently acting alongside UCB partner Matt Walsh in a new half-hour comedy series on Spike TV called Players, which was created by Walsh. Roberts and Walsh star as two brothers who run a sports bar. The series began airing on March 2, 2010.

Roberts has written several screenplays with writing partner Jay Martel, one of which was recently sold to DreamWorks, with Steven Brill in talks to direct.

Roberts lives in Agoura Hills, California with his wife Katie and their two children.