After appearing in the short, "A Director Talks About His Film". Riegert made his feature film debut as one of the denizens of "National Lampoon's Animal House" (1978). He followed as John Heard's best friend in Joan Micklin Silver's "Chilly Scenes of Winter/Head Over Heels" (1979). Riegert turned in a memorable, understated performance as an oil company employee in Bill Forsyth's wry satire, "Local Hero" (1983). Reuniting with Joan Micklin Silver, he was quite affecting as a pickle salesman chosen for a book editor (Amy Irving) by a matchmaker in "Crossing Delancey" (1988). Riegert also delivered solid support as a policeman chasing Jim Carrey in "The Mask" (1994) and a hit man training a new recruit in "Coldblooded" (1995).
Riegert earned mixed reviews for his turn as a young Richard M. Nixon in the award-winning "Concealed Enemies" (1984), a PBS docudrama about the Alger Hiss case. Exhibiting an ingratiating presence, he delivered a change of pace turn as an immigrant songwriter (loosely inspired by Irving Berlin) in the 1984 CBS miniseries "Ellis Island", Attempting to find series stardom, he accepted a leading role in John Byrum's acclaimed but little-seen CBS series "The Middle Ages" (1992). Bouncing back, Riegert earned a supporting Emmy nomination for his performance as a stockbroker arranging a deal in the HBO movie "Barbarians at the Gate" (1993) and then displayed his singing abilities opposite former girlfriend Bette Midler in the TV remake of "Gypsy" (CBS, 1993). More recently, Riegert has been cast in fatherly roles (as in the independent films "Infinity" and "Pie in the Sky" both 1996). He returned to the Broadway stage in 1997, first as the cheating husband of a political appointee in Wendy Wasserstein's "An American Daughter" and later as Bobby Gould in David Mamet's "The Old Neighborhood".
2000 proved to be a banner year for the actor who landed a key role in the ensemble of the hit film "Traffic" (2000) and a recurring part on the popular HBO series "The Sopranos". But perhaps his most notable accomplishment that year was making his directorial debut with the Oscar-nominated live-action short "By Courier".