His early film credits include Underground Aces, Longshot, Back Roads, Just Before Dawn (all 1981).

[2] Seymour relocated to New York City, where he appeared on Broadway as Alan Strang in a production of Peter Shaffer's Equus between 1976 and 1977.

[2] He appeared in the short-lived sitcom Makin' It (1979)[3] before making his film debut in Underground Aces (1981).

[4] Next, he co-starred with Leif Garrett and Linda Manz in the television film Longshot (1981), about a group of teenage foosball players.

[4] Other film roles include in the horror-comedies Ghoulies (1985) and Killer Party (1986), the drama Empire of the Sun (1987), and the comedy-drama Rain Man (1988).