He appeared in the Metropolitan Opera's chamber production of Virgil Thomson's Four Saints in Three Acts and with New York City Opera, Austria's Graz Opera, and Milwaukee's Florentine Opera, as well as the New York Philharmonic, Chicago Symphony, Baltimore Symphony, and other orchestras.

His repertoire included the roles of Mephistopheles in Faust and Porgy; solo roles in cantatas and oratorios by Handel, Bach, and Mendelssohn; and African-American spirituals and work songs. He appeared in recital at Carnegie Hall in 1986.

In 1973, Matthews co-founded Ebony Opera, a New York-based company devoted to African-American operatic repertoire; he served as artistic director until his death. The company's many premieres included Matthews' Oh Freedom, written with Lena McLin, and Journin'.