Forte was born in Alameda County, California, the son of Patricia C. (née Stivers) and Orville Willis Forte III. He was raised in Lafayette, California, and graduated from Acalanes High School and UCLA with a history degree. While at UCLA, he was a member of the Lambda Chi Alpha fraternity.
Forte joined the cast of Saturday Night Live in 2002 as a featured player. He was upgraded to full cast member the next season. On August 26, 2010, Forte announced that he would be leaving SNL after eight years on the show (2002–2010) to focus on other projects. On April 2, 2011, he made a guest appearance on the show, reprising his role of Greg Stink.
Before joining SNL, Forte was a member of The Groundlings. He has written and/or produced on the television series 'Late Show with David Letterman', '3rd Rock from the Sun', 'That 70s Show', and Action. Forte provided the voice of Abe Lincoln and the show announcer on the critically acclaimed but short-lived animated series, Clone High. He was a consultant on another short-lived animated series, God, the Devil and Bob.