He appeared in the films Uncommon Valor, Air America, Volunteers, Who's Harry Crumb?, Iron Eagle, and Fear and Loathing in Las Vegas.
He appeared in comedy clubs, including The Bitter End in Greenwich Village, The Improv in Los Angeles, and Catch a Rising Star in New York City.
In Los Angeles, he became a regular at the Comedy Store and the Improv and made numerous appearances on television variety shows and in Las Vegas.
Thomerson first came to prominence in the short-lived comedy science-fiction TV series, Quark in 1977–78, as Gene/Jean, a character of dual gender who randomly switched between the two.
When Charles Band started Full Moon Features in the late 1980s, one of his first projects was the sequel Trancers II (1991), in which he reunited Thomerson with much of the cast from the first film.