William Demarest started in show business working in vaudeville, appearing with his wife as “Demarest and Colette”, then moved on to Broadway. Demarest worked regularly with director Preston Sturges, becoming part of a “stock” troupe of actors that Sturges repeatedly cast in his films. He appeared in ten films written by Sturges, eight of which were under his direction, including The Lady Eve, Sullivan’s Travels and The Miracle of Morgan’s Creek. Demarest appeared with veteran western film star Roscoe Ates in the 1958 episode “And the Desert Shall Blossom” of CBS’s Alfred Hitchcock Presents. In the story line, Ates and Demarest appear as old timers living in the Nevada desert. The local sheriff, played by Ben Johnson, appears with an eviction notice, but he agrees to let the pair stay on their property if they can make a dead rosebush bloom within the next month. In 1959, William Demarest was named the lead actor of the 18-week sitcom Love and Marriage on NBC in the 1959–1960 season. Demarest played William Harris, the owner of a failing music company who refuses to handle popular rock and roll music, which presumably might save the firm from bankruptcy. Joining Demarest on the series were Jeanne Bal, Murray Hamilton and Stubby Kaye. Demarest appeared as Police Chief Aloysius of the Santa Rosita Police Department in the film It’s a Mad, Mad, Mad, Mad World (1963), as well as on a memorable episode (“What’s in the Box”) of Rod Serling’s The Twilight Zone as a hen-pecked husband driven to the murder of his wife.

His most famous television role was in the ABC and then CBS sitcom My Three Sons from 1965 to 1972, playing Uncle Charley O’Casey. He replaced William Frawley, whose failing health had made procuring insurance impossible. Demarest had worked with Fred MacMurray previously in the films Hands Across the Table (1935), Pardon My Past (1945), On Our Merry Way (1948), and The Far Horizons (1955) and was a personal friend of MacMurray. Also, he worked with Irene Dunn in “Never a Dull Moment.” William Demarest was married twice. His first wife was his vaudeville partner Estelle Collette (26 October 1886–19 Nov 1968), born Esther Zichlin. Demarest helped raise her daughter from her earlier marriage to poet and novelist Samuel Gordon (10 September 1871 – 10 January 1927), author Phyllis Gordon Demarest (b. 31 March 1908). His second wife was Lucile Thayer (30 Sep 1912–16 Oct 2009), born Lucile Theurer, daughter of Herman Theurer and Lillie Sjoberg, who due to her activism on health issues in the motion picture industry in October 1960 was named California Lay-Chairman of the ANA fundraising campaign. Demarest’s favorite recreations were hunting, fishing, golf and playing the cello. William Demarest died in Palm Springs, California and was interred in Glendale’s Forest Lawn Memorial Park. At the time of his death, he was suffering from prostate cancer and pneumonia.