Schoenbaum began his career as an actor, and helped start up the Trinity Repertory Theatre in Providence, Rhode Island, in 1963. He had a long association with the Guthrie Theater, starting out as its Associate Manager in 1966, and serving as its Managing Director from 1969 to 1986. In 1982, under his management, the Guthrie received the regional Tony Award.

He served as President of the League of Resident Theaters (LORT) from 1977 to 1981, and throughout his career, also held positions with Theatre Communications Group, the National Endowment for the Arts, the American Arts Alliance, and other organizations.

He retired to Florida, where he continued his involvement in theater, serving on the board of directors of Asolo Rep Theatre.