He was married to Ida Lupino from 1951-1984.
Howard Duff made an uncredited appearance as Sam Spade (albeit without mentioning the character's last name) in the Dec. 5, 1946 episode of Suspsense, "The House in Cypress Canyon." Both Suspense and Sam Spade were produced by William Spier, who arranged for Duff's cameo.
Duff has a star on the Hollywood Walk of Fame at 1625 Vine Street.
Howard Duff appeared with his daughter, Bridget, in the 1954 film Private Hell 36.
Howard Duff played the title character on The Adventures of Sam Spade, Detective on radio from 1946 to 1951.
Howard Duff: Becoming Sam Spade was the greatest moment in my life. It just goes to prove what luck can happen to a guy when he least expects it.
Howard Duff: (on auditioning for Sam Spade on radio) There must have been at least 100 other guys jammed in that office waiting to read. I even recognized a few famous faces in the crowd, and it threw me into even a greater melancholy. By the time my turn came I was feeling real mean and about as low as a patrolman's instep. When they handed me the script and told me to go ahead, I delivered the lines in a half-snarling, half-bored manner like a guy reading a grocery list.