Although Labyorteaux made his acting debut at the tender age of three, it wasn't until he was a more seasoned nine-year-old that he broke into film. In 1974, he landed the role of Peter, grandnephew to Lucille Ball's character, in the film "Mame", as well as a small part in the ABC TV-movie "Only With Married Men". After numerous appearances on series like "Starsky and Hutch" and "The Love Boat", the young actor was offered the chance to join the cast of the beloved pioneer drama "Little House on the Prairie" as Andy Garvey, Albert Ingalls' quiet, sensitive best friend. The close nature of the boys' on-screen relationship wasn't hard to convey since Labyorteaux's co-star was also his real-life little brother Matthew. He remained with the series for four seasons and was one of the actors who remained when the show was retooled for its final year airing as "Little House: A New Beginning".
Although life after "Little House" proved to be a bit of a trial, with few quality parts coming Labyorteaux's way, he continued to work even if it was sporadically. He proved an effective supporting player in TV movies like "Young Joe: The Forgotten Kennedy" (ABC, 1977), "The Comedy Company" (CBS, 1978) and "The Prince of Bel-Air" (ABC, 1986), a romantic comedy that starred Mark Harmon, Kirstie Alley and Dean Cameron. Labyorteaux reteamed with the trio for a second lightweight, likable outing, this time the 1987 big-screen flick "Summer School". In 1989, he had small roles in two high-profile entertainments: the feature film "Heathers" and the popular TV show "21 Jump Street". In the former black comedy, he played a rude, bullying high school football star who lives to regret talking trash about classmates Winona Ryder and Christian Slater while in the Fox cop show, he effectively played a disillusioned, AWOL soldier whom the baby-faced officers are charged with returning to his barracks before he is deemed a deserter.
The early 1990s saw Labyorteaux in a variety of low-budget, critical disasters such as "Ski School" (1991), "Ghoulies III: Ghoulies Go to College" (1992) and "National Lampoon's Last Resort" (1994), which he co-wrote and which starred the infamous--and inseparable--Corey Haim and Corey Feldman. The actor's boyish dark good looks and talent for playing second banana were better used by the Groundlings comedy troupe which employed him as a writer and performer. He also fared well doing voiceovers for commercials and animated shows like Fox's "Spider-Man: The Animated Series".
The actor began paving his way back to series TV in 1995 when he filmed a pilot for the military mystery show "JAG". He was not invited to join the cast, however, until 1997 when the series moved from NBC to CBS. Series creator and executive producer Donald Bellisario liked the comic relief Labyorteaux's character provided in the pilot so much he decided to make lawyer Lt. Bud Roberts a regular on the show.