A graduate of San Francisco State University, where he studied acting, and Wayne State University, where he got his masters degree, Tambor most recently starred in the television comedy Arrested Development in a dual role as twin brothers, "George Bluth Sr." and "Oscar Bluth." He has also starred in The Larry Sanders Show as hapless co-host Hank Kingsley, Hellboy as an arrogant boss disgusted of his clandestine employee, How the Grinch Stole Christmas and There's Something About Mary. Tambor has been an actor for over three decades, and has 100 credits to his name. In the spring of 2005, he starred as George Aaronow in the Broadway revival of David Mamet's Pulitzer Prize-winning play Glengarry Glen Ross. He's also remembered for his several guest appearances as different characters on Three's Company and its spinoff The Ropers with its spinoff star Norman Fell. He is also the voice of King Neptune in The SpongeBob SquarePants Movie. In 2006 Jeffrey portrayed George Washington on the family friendly podcast The Radio Adventures of Dr. Floyd.

In December of 2004, Tambor's wife, Kasia, gave birth to their son Gabriel on December 10 and his daughter, Molly, gave birth to her son, Mason, on December 14.

In addition to acting, Tambor announced for the game show Hollywood Squares from 2002 to 2003.

For several years, Jeffrey has also taught a popular class for actors, based on his availability. He was formerly a longtime teaching associate of famed acting coach Milton Katselas.

In April 2006, Tambor signed on to a series with John Lithgow called Twenty Good Years about two men who ponder the last 20 years of their life. The show will air on NBC, but it is unclear when.