His first film roles were in 1955. He appeared as a student in The Blackboard Jungle (billed as Jameel Farah) and as a fruit vendor in Kismet (uncredited).

He was hired for one day's work as "Corporal Klinger" on the M*A*S*H episode "Chief Surgeon Who?" and he played it so well that this day job became an eleven year career. His character wore dresses to try and convince the army that he was crazy and he deserved a Section 8 discharge. He was asked back for a dozen episodes in the second season and he became a regular in the third.

Farr's first acting success occurred at age eleven when he won $2 in a local acting contest. After a stellar high school career when he was one of the standouts among his class, Farr attended the Pasadena Playhouse where an MGM talent scout discovered him, offering him a screen-test for The Blackboard Jungle. He won the role of the mentally retarded student, Santini.

Although Farr was off to a promising start, roles were infrequent for the young actor, and he took jobs as a delivery person, a post office clerk, an army surplus store clerk, an airlines reservations agent and as an employee at a chinchilla ranch.

Farr began to carve his niche in television when, in the late 1950s, he became a regular on The Red Skelton Show before graduating to second banana with Harvey Korman on The Danny Kaye Show. Farr also appeared on The Dick Van Dyke Show and was a regular on The Chicago Teddy Bears before being asked to play the role of "Corporal Klinger" on M*A*S*H.

After the enormously successful comedy finished its eleven year run, Farr and co-stars Harry Morgan and William Christopher spent two years starring in AfterMASH, the sequel that explored how civilian life treated their characters. This lasted for only 2 seasons.

While working on M*A*S*H, Farr found time to do some work on the silver screen. He appeared in Cannonball Run and Cannonball Run II.

He also appeared in several made-for-TV movies such as Murder Can Hurt You, Return of the Rebels, and For Love or Money as well as in guest-starring in Kolchak: The Night Stalker.

Farr endorsed the U.S. Mars bar in commercials during the 1980s.

This son of a Lebanese Antiochian Orthodox Toledo, Ohio grocer received a Star on the Hollywood Walk of Fame in 1985.

He is one of only two actors from M*A*S*H who has written an autobiography (the other one is Alan Alda); Jamie's autobiography is titled Just Farr Fun.

He is also the only major M*A*S*H performer to have actually served in the military during the Korean War era. He never saw combat though having spent the entire war stationed in Japan.

Farr is still active in regional theater and guest stars occasionally on different TV series. He also has a yearly women's golf LPGA tournament, The Jamie Farr Owens Corning Classic, presented by Kroger in northwest Ohio since 1984.

He hosts this annually. It was originally called the Jamie Farr Toledo Classic before 1996, and the Jamie Farr Kroger Classic until 2004.

The park where Jamie Farr used to hang out when he was younger was renamed "Jamie Farr Park" in his honor on July 5, 1998. About the park, he said, "I wanted to be an actor, a famous actor, and I wanted my hometown of Toledo, Ohio to be proud of me", Farr told about 400 admirers and was quoted in The New York Post: "Jamie Farr Park is certainly a highlight of my life and career."