The son of ballet dancers, Thomas began his career as a juvenile performer making his Broadway debut at age seven as one of the Roosevelt children in the award-winning play "Sunrise at Campobello" (1958). Additional stage roles followed including John Henry in "The Member of the Wedding" (1959), Eric in "The Playroom" and the two young princes killed by "Richard III" in separate productions: in 1964, he was the young Prince of Wales at Stratford, CT and in 1966, the Duke of York in NYC's Central Park. As an adult, Thomas has stretched his talents in both classical plays (i.e., "Hamlet", "The Count of Monte Cristo", "Richard III") and contemporary works (e.g., "Fifth of July", "The Lisbon Traviata").
Thomas began appearing on TV in the late 1950s with the "Hallmark Hall of Fame" production "A Christmas Tree" (NBC, 1959). With Jack Lescoulie, he co-hosted the children's educational series "1, 2, 3, Go!" (NBC, 1961-62) and then moved to work on daytime, appearing in the ABC soap opera "Flame in the Wind/A Time for Us" and the CBS drama "As the World Turns". In 1971, Thomas was cast as John-Boy opposite Patricia Neal in the special "The Homecoming" (CBS). The following season, he began his five year stint as the oldest child of a rural Virginia family coping with the effects of the Depression. The tall, lanky blond actor with the distinctive facial birthmark brought a warm, eager-to-please charm to the role which earned him an Emmy Award. He subsequently went on to appear in a variety of TV-movies and specials, notably portraying the title role in "Living Proof: The Hank Williams Jr. Story" (NBC, 1983), a scheming evangelist in "Glory! Glory!" (HBO, 1989), the lover of a man who has died from AIDS in "Andre's Mother" (PBS, 1990) and a threatening ex-convict in "Down, Out & Dangerous" (USA, 1995).
After making his film debut as Joanne Woodward's son in "Winning" (1969), Thomas went on to earn praise for his leading performances as callow youths in Frank Perry's "Last Summer" (also 1969) and "Red Sky at Morning" (1971). While he possessed a pleasant screen presence, Thomas was never able to fully remove himself from his TV persona. His post-"Waltons" feature outings have been sporadic and mostly in less than successful ventures that did not tax his abilities.