[1] He also voiced the mandrill Rafiki in The Lion King, and played Isaac Jaffe in Aaron Sorkin's dramedy Sports Night.

Guillaume was the first African-American actor to portray the title role in Andrew Lloyd Webber’s The Phantom of the Opera.

[6] His other stage appearances included Golden Boy (with Sammy Davis Jr.),[7] Tambourines to Glory, Guys and Dolls, for which he received a Tony Award nomination,[8] Jacques Brel is Alive and Well and Living in Paris, and Purlie.

[4] In 1964, Guillaume portrayed Sportin' Life in a revival of Porgy and Bess at New York City Center.

[3] He recorded an LP album, Columbia CS9033, titled Just Arrived, as a member of The Pilgrims, a folk trio, with Angeline Butler and Millard Williams.

[5] Columbia records producer Tom Wilson had set out to create the Pilgrims as an answer to the popular folk trio Peter, Paul and Mary.

[10] In 1976, Guillaume played Nathan Detroit in the Broadway revival of Guys and Dolls and was nominated for a Tony Award.

[11] In 1990, Guillaume was cast in the Los Angeles production of The Phantom of the Opera, replacing Michael Crawford in the title role.

[3] He also appeared as marriage counselor Edward Sawyer on The Robert Guillaume Show (1989), Detective Bob Ballard on Pacific Station (1991–1992), and television executive Isaac Jaffe on Aaron Sorkin's short-lived but critically acclaimed Sports Night (1998–2000).

[3] In 1999, Guillaume suffered a stroke while working on Sports Night at Walt Disney Studios in Burbank, California.