He began acting professionally at age 13 and was soon cast as Louis Plumb on the short-lived NBC series Hull High.
In 1993, Belafsky took some time off from acting to attend Brown University, where he honed his comedic skills in the improvisation comedy troupe, Improvidence.
Dangerfield hand-picked Belafsky to be his opening act at the MGM Grand in Las Vegas and later gave him starring roles in two of his films, Back By Midnight and The 4th Tenor.
Since then, Belafsky has been featured in such films as Pearl Harbor, Evolution, America's Sweethearts, Back by Midnight, Men in Black II, A Mighty Wind and Funny Money.
He has also been featured on television, including a series regular role in MTV's The Lyricist Lounge Show, as well as guest appearances on Still Standing, Six Feet Under and Boston Legal.