His first film was the 1982 comedy The Last American Virgin, in which he starred as Gary. His other well-known film roles are in the 1984 horror movie Friday the 13th: The Final Chapter as Ted, and the 1985 hit drama movie Mask as Ben. His most recent film is 2009's His Name Was Jason: 30 Years of Friday the 13th. He was nominated for a Cable Ace Award along with Richard Gere and Ian McKellen for his one-scene performance in HBO's And the Band Played On based on Randy Shilts' acclaimed book on the epidemiology of the AIDS epidemic.
Monoson starred in the short lived 1990s TV series Prince Street. He also has made guest appearances on a number of TV shows, including Diff'rent Strokes, Beverly Hills, 90210, ER, NCIS, CSI: Crime Scene Investigation, 24, Without a Trace, Seven Days, the Star Trek: Deep Space Nine episode "The Storyteller", and the Star Trek: Enterprise episode "Fortunate Son".