Born in York, Pennsylvania, Sheffer had a passion for acting even at a young age. He won the Best High School Actor Award in a state-wide competition. He studied Theater at East Stroudsburg University, where he played Valere in a production of Moliere's Tartuffe. Immediately after graduation, Sheffer relocated to New York to pursue a career in acting.

Early auditions landed him a role in the off-Broadway play Punchy. Soon after, he found himself co-starring in the award-winning Broadway production Torch Song Trilogy. In less than a year, producers spotted his work on Broadway and cast him in his feature film debut in That Was Then, This Is Now, opposite Emilio Estevez. Sheffer also starred in the Vietnam based play G.R. Point, and won the LA Critics Drama Desh Award for his performance.

Sheffer went on to starring roles in the John Hughes comedy Some Kind of Wonderful and the father/son drama Split Decisions, with Gene Hackman. He followed that with the lead role in Robert Redford's critically acclaimed film A River Runs Through It, opposite Brad Pitt. Other film credits have included the hard-edged drama The Program, Sleep With Me and Wings of Courage. In addition, he starred with Lawrence Fishburn and Alfre Woodard in the Emmy Award-winning HBO special Miss Evers' Boys.