Silvera left Northeastern Law School in 1934, when he was cast in Paul Green's production of "Roll Sweet Chariot". He next joined the New England Repertory Theatre where he appeared in productions of "MacBeth", "Othello" and "The Emperor Jones". He also worked at Federal Theatre and with the New Hampshire Repertory Theatre. In 1940, Silvera made his Broadway debut in a small role in "Big White Fog". His career was interrupted in 1942, when he enlisted in the United States Navy during World War II. He was assigned to Camp Robert Smalls, where he and Owen Dodson were in charge of entertainment. Silvera directed and acted in radio programs and appeared in USO shows. Honorably discharged at the war's end in 1945, he joined the cast of "Anna Lucasta" and became a member of the Actors Studio.