Singer was born in Vancouver, British Columbia into a family of performers. His father, Jacques Singer, was a symphony conductor, and his mother, Leslie, a concert pianist. Singer's sister, Lori Singer, is also an actress (Ariel in Footloose). Marc was raised in Corpus Christi, Texas. His cousin is director Bryan Singer of Superman Returns and X-Men.

Singer has appeared in several fantasy adventure films and series, such as The Beastmaster and its sequels, in which he played the title role, and as Mike Donovan in the 1983 mini-series V, the 1984 sequel V: The Final Battle, and the TV series V: The Series.

Other roles include the 1982 film If You Could See What I Hear (where he portrayed blind musician Tom Sullivan), Body Chemistry, Something for Joey (as football star John Cappelletti), Watchers II, High Desert Kill, The Fighter, Go Tell the Spartans and Dead Space, as well as General Klaus Von Kraut in A Man Called Sarge.

Singer voiced the character of Man-Bat on Batman: The Animated Series. He has guest-starred on television series, such as Dallas, The Twilight Zone, The Hitchhiker, Murder, She Wrote, The Young and the Restless, The Ray Bradbury Theater and Highlander: The Series.

Singer is active in theater and played Petruchio in the American Conservatory Theatre (ACT) production of Shakespeare's Taming of the Shrew. He also played Christian in ACT's Cyrano de Bergerac. Both Taming of the Shrew and Cyrano were filmed.

Singer is currently teaching kids inter-disciplinary tactics at the Heifetz International Music Institute, which is located in Wolfeboro, New Hampshire.

Singer was the first choice for the role of Conner MacLeod in Highlander, but he turned it down due to his commitment on V: The Series.