Larson's first TV-movie was as swinging bachelor Bill Bixby's unexpected teenaged son in "Congratulations, It's Boy!" (ABC, 1971). He went on to appear in "All My Darling Daughters" (ABC, 1972) and its 1973 sequel and the wayward girls' home classic "The Girls of Huntington House" (ABC, 1973). His big screen career got off to an unpromising start with "The Student Nurses" (1970) and slogged along with a small part in "The Magnificent Seven Ride" and a lead role in the low-budget "Outside In" (both 1972).
In 1973, Larson became fed up with film and TV and for the next decade concentrated on acting and directing in California theater productions. He appeared in everything from major L.A. Equity shows to tiny experimental workshops in storefronts. Larson had the title role in Shakespeare's "Henry IV, Part 1" and was featured in "Dominicus Marlowe", Sam Shepard's "Action" and a play about stunt pilot and film star "Ormer Locklear". Among his directing credits are the L.A. productions of "Are You Lookin'?" and the Sam Shepard/Patti Smith play "Cowboy Mouth". He and Murray Mednick collaborated on the multi-play, seven-year series "Coyote Project". Larson was also in at the beginnings of such companies as the Provisionals, the Odyssey, the Gene Dynarski and Santa Monica's Powerhouse Theater.
In 1979, Larson began to accept film and TV projects again, though he never gave up his theatrical work. He returned to films with a small part as a demonstrator in James Bridges' "The China Syndrome" (1979) and since then has appeared in more than a dozen films: mostly, large roles in small films and small roles in large ones. His lesser roles have included appearances as Louella Parsons' spy in "Frances" (1982), a security technician in Natalie Wood's swan song "Brainstorm" (1983), a flight attendant in Stephen Frears' "Hero" (1992) and a neighbor to Sally Field and Ed Harris in John Schlesinger's "Eye for an Eye" (1996). Larson has played leads in smaller films, but none of them has really caught on with the public. He reteamed with James Bridges to play a junkie in the mystery "Mike's Murder" (1982) and went on to star in the disaster film "City Limits" (1985) and the detective thriller "Dead Aim" (1987).
Larson has also appeared in a number of TV-movies and series, beginning with the miniseries "Studs Lonigan" (NBC, 1979). His TV-movies have included the courtroom drama "The Last Innocent Man" (HBO, 1987), the sudsy "Mistress" (CBS, 1987) and "Danielle Steele's 'Fine Things'" (NBC, 1990), "Proudheart" (TNN, 1993) and "The Gambler V: Playing for Keeps" (CBS, 1994). He was also a regular on the short-lived series "Morningstar/Eveningstar" (CBS, 1986), as a social worker, and "Heartbeat" (ABC, 1988-1989), as a fertility specialist. Larson has continued to turn up as a guest on numerous series like "L.A. Law", "Matlock", "Designing Women" and "Party of Five".