A native of San Antonio, TX, Thomas knew he wanted to act from the age of five. At age eight, he persuaded his mother to take him to a local casting call. This lead to his debut at ten in "Raggedy Man" (1981), as Sissy Spacek's son, and his TV debut in "The Steeler and the Pittsburgh Kid" (NBC, 1981), based on a Coke commercial. His first project after "E.T." was "Misunderstood" (1984), a powerful drama about the reconciliation between a newly widowed father (Gene Hackman) and his estranged young son. Thomas proved capable of meeting the emotional demands of the material. His follow-up, "Cloak and Dagger" (1984), a clever Hitchcockian thriller conveniently shot in San Antonio, would be his last Hollywood film for nearly a decade. Thomas starred in the likable Australian adventure "Frog Dreaming/The Quest" (1985) before taking four years off from acting.

Thomas returned to the screen in "Murder One" (1988), a Canadian feature about three young prison escapees who get involved with mass murder after stealing a car. He proved capable in period fare as the amorous young music teacher who gets manipulated in Milos Forman's "Valmont" (1989). With a flair for playing lonely, introverted youths, Thomas was an apt and interesting choice to play the young Norman Bates in "Psycho IV: The Beginning" (Showtime, 1990). His other TV-movies have included "Curse of the Starving Class" (Showtime, 1995), as Raymond Buckey, one of the hapless defendants, in "Indictment: The McMartin Trial" (HBO, 1995) and "Riders of the Purple Sage" (TNT, 1996).

Thomas returned to US features in a supporting role in the rough-hewn UFO drama "Fire in the Sky" (1993). He had a more sizable role in the period drama "Legends of the Fall" (1994), as the idealistic younger brother of Aidan Quinn and Brad Pitt who has his mettle tested on the battlefields of WWI. In the comedy "Hijacking Hollywood" (1996), he played an over-zealous would-be filmmaker. Thomas made impressive turns in the indie features "Niagara, Niagara" (1997) and "The Suicide Kings" (1997), and the actor continued to nab character roles in both non-studio efforts--including the crime thriller "Fever" (1999), "The Quickie" (2001) and "Dead In the Water" (2001)--as well as more glossy projects--such as his role as Ishmael in the USA Network miniseries "Moby Dick" (1998), the dark Showtime comedy "The Happy Face Murders" (1999) and the Billy Bob Thornton-directed "All the Pretty Horses" (2000). In 2002 Thomas appeared as 1860s gang member Johnny Sirocco in director Martin Scorsese's bloody period drama "Gangs of New York."