Mantooth has appeared in numerous films and television series in lead and supportive roles including miniseries adaptations of "Testimony of Two Men" (1977) and a starring role as Abraham Kent in "The Seekers" (1979). Through the 1990s and 2000s, he appeared in daytime soap operas, earning him four Soap Opera Digest Award nominations. He frequently returns to performing in theatrical productions. He serves as an associate artist at Jeff Daniels' Purple Rose Theatre. His performances includes Mark Kaufman's "Evil Little Thoughts", "Black Elk Speaks", Carey Crim's "Morning after Grace", Lanford Wilson's "Rain Dance", and innumerable works by Native American playwrights including William S. Yellow Robe, Jr.