His television credits include a leading role as Phillip Drummond in the sitcom Diff'rent Strokes (1978–1986), as Dr. Arthur Harmon on Maude (1972–1978), and as Charlie Ross in Mr. President (1987–1988).

[3] After a stint at the Stratford Festival in Canada, Bain had further success as a stage actor in the 1956 revival of Eugene O'Neill's The Iceman Cometh.

"[5] Bain's Broadway theatre credits include Candide, Advise and Consent, An Enemy of the People, Uncle Vanya, and On Borrowed Time.

[8] In the early 1970s, Bain appeared in New York–based films like Lovers and Other Strangers and Woody Allen's Bananas before achieving national recognition for his work in television.

He then starred in Diff'rent Strokes (1978–86) as Park Avenue millionaire Phillip Drummond, who adopted two African-American orphaned boys from Harlem, Willis and Arnold, to live with him and his daughter, Kimberly, and housekeeper, Mrs. Garrett.

In 1996, Bain reprised his role of Phillip Drummond alongside Gary Coleman as Arnold Jackson on the series finale of The Fresh Prince of Bel-Air.