Born in San Pedro, California, Muldoon began his acting career while studying at the University of Southern California, where he also turned out for its football team called the Trojans.
After graduating in 1991, he landed a recurring role as Jeffrey Hunter on the high school sitcom Saved By the Bell.
But it was on Days of Our Lives that he made his breakthrough, later going on to play the villain Richard Hart in Melrose Place for three seasons, between 1995 to 1996, before hitting the big screen.
Away from the camera, Muldoon – who had a band called The Sleeping Masses – also worked behind the scenes, producing films such as The Tribes of Palos Verdes, Arkansas and Marlowe.
And he was set to produce the upcoming feature Kockroach, starring Chris Hemsworth.
His last big on-screen appearance will come in the forthcoming action-crime thriller, Dirty Hands, opposite another of his Starship Trooper co-stars, Denise Richards.
Muldoon is survived by his partner, Miriam Rothbart, external; parents Deanna and Patrick Muldoon Sr, his sister and brother-in-law Shana and Ahmet Zappa, niece Halo and nephew Arrow Zappa.