Turning to acting in the 1970s, Seneca managed to debut in a big way, in the Broadway production of "Of Mice and Men" starring James Earl Jones. He later was featured in the Broadway and touring productions of "The Little Foxes," starring Elizabeth Taylor (1981), and co-starred in August Wilson's award-winning "Ma Rainey's Black Bottom" (1984). Seneca made his TV debut in "With All Deliberate Speed" (CBS, 1976), about school desegregation, and went on to appear in "Wilma" (NBC, 1977), the biopic of athlete Wilma Rudolph, "Terrible Joe Moran" (CBS, 1984), with James Cagney and Art Carney, and "A Gathering of Old Men" (CBS, 1987), with Louis Gossett Jr. Seneca was a guest performer on numerous shows from "Amazing Stories" and "The Equalizer" to the comedic "The Cosby Show" and "The Golden Girls."Although he had a bit part as a party guest in Robert Benton's "Kramer vs. Kramer" (1979), Seneca's feature film career did not take off until the 1980s. Sidney Lumet cast him as Paul Newman's medical expert in "The Verdict" (1982) and he had a meaty role as teacher-singer Willie Brown in "Crossroads" (1986). Seneca was a scientist destroyed by "The Blob" and the college president in Spike Lee's "School Daze" (both 1988). He went on to appear in Lee's "Mo' Better Blues" (1990) and "Malcolm X" (1993). He also earned critical applause for his turn as Spits in "The Saint of Fort Washington" (also 1993). Seneca's final screen role was as Reverend Sweet in Joel Schumacher's "A Time to Kill" (1996).