Conrad Bain was born in Lethbridge, Alberta, the son of Jean Agnes (née Young) and Stafford Harrison Bain, who was a wholesaler. He studied at the Banff School of Fine Arts before serving in the Canadian Army during World War II. He later studied in New York at the American Academy of Dramatic Arts, graduating in 1948; one of his classmates was comedian Don Rickles. Bain became a naturalized citizen of the United States in 1946. Bain died of natural causes on January 14, 2013, in Livermore, California, three weeks before his 90th birthday.

Bain had two sons and a daughter with Monica Sloan, to whom he was married in 1945 until her death in 2009. His identical twin brother is actor Bonar Bain, who once played Arnold Harmon, the twin brother of Conrad’s Maude character, Dr. Arthur Harmon. Despite a popular misconception, Conrad was not related to fellow performer Barbara Bain.

After a stint at the Stratford, (Ontario), Shakespeare Festival, Bain had further success as a stage actor in the 1956 Broadway revival of Eugene O’Neill’s The Iceman Cometh. The New York Times reviewer noted that his role was “especially well acted.” Bain’s other Broadway theatre credits include Candide, Advise and Consent, An Enemy of the People, Uncle Vanya, and On Borrowed Time. On Off Broadway, he appeared in the original run of Steambath. While doing stage work in New York City, Bain also found work on television, appearing in the soap opera Dark Shadows as the town inkeeper, Mr. Wells, during seasons 1 and 2. His character was killed off by werewolf Chris Jennings (Don Briscoe).

In the early 1960s, Bain was one of the principal organizers of the Actors Federal Credit Union. In an article in the Credit Union Times, he recalled that “the effort grew out of the fact that, at least in the world of financial services, actors and other performers got no respect and, more importantly, no access to credit.”  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 is best known for his roles as Dr. Arthur Harmon, Bea Arthur’s title character’s conservative nemesis, who married her best friend, Vivian, in Maude (1972–78) and as Park Avenue millionaire Phillip Drummond in Diff’rent Strokes (1978–86), in which he adopted two African-American orphaned boys from Harlem, Willis and Arnold, to live with him and his daughter, Kimberley, and housekeeper, Mrs. Garrett. In 1979, he played Phillip Drummond in an episode of The Facts of Life. In 1996, Bain reprised his role of Phillip Drummond along with Gary Coleman as Arnold Jackson on the series finale of The Fresh Prince of Bel-Air.