[1] Hesseman attended the University of Oregon, and was later a founding member of the San Francisco-based improvisational comedy troupe The Committee with fellow actor David Ogden Stiers.

Early in his acting career, he used the alias Don Sturdy, the name he also used as a radio DJ[2] on underground FM station KMPX in San Francisco in the late 1960s.

[3] Under the alias of Don Sturdy, Hesseman made his first television appearances, including the episode "Public Affairs: DR-07" of the show Dragnet in 1968.

On July 18, 1969, he appeared with the improvisational comedy group The Committee in several sketches on The Dick Cavett Show, including one with guest Janis Joplin.

He portrayed Sam Royer, the man who married Ann Romano (Bonnie Franklin) on the sitcom One Day at a Time from 1982 to 1984.

He made three appearances on Saturday Night Live, one in which he paid tribute to, and told jokes about, the recently deceased John Belushi and the other in which NBC showed a picture of U.S. President Ronald Reagan, which Hesseman mooned off-camera.

[citation needed] In 1995, Hesseman played the role of the Marquis de Sade in Quills at the Geffen Playhouse in Westwood, California, which included one scene in which he was fully naked.

In February 2011, he portrayed Dr. Elliot D. Aden in the 11th-season CSI: Crime Scene Investigation episode "Turn On, Tune In, Drop Dead.” Dr. Aden was head of Department of Defense project called Stonewall at WLVU, which did research in fringe psychological concepts such as extrasensory perception and out-of-body experiences.