Born in Susanville, California, Cady attended Stanford University, where he was involved with the campus humor magazine, the Stanford Chaparral. He served in the United States Army Air Forces during World War II.

Cady began acting in 1947. In 1950 he had an uncredited speaking role in the classic film noir drama D.O.A. (as Sam the bartender in Banning, California) and another uncredited role in Father of the Bride requesting a martini from Spencer Tracy during the engagement party. He also had a small part in the 1950 noir classic The Asphalt Jungle playing a witness that refused to identify a robbery suspect. He appeared in George Pal's 1951 film When Worlds Collide (as the assistant who pushes the wheelchair belonging to John Hoyt's character). Cady had a prominent role in Billy Wilder's film Ace in the Hole (also known as The Big Carnival). He had a small non-speaking role, seen mostly in long shot, in one of Alfred Hitchcock's most prestigious films, Rear Window. Cady also played the husband to Eileen Heckart's character in The Bad Seed. He had a small speaking role, coming to pick up his distraught but very drunk wife from the home of their daughter's school friend, the last person to see their son alive before he drowned.

In the 1950s Cady played Doc Williams in Ozzie and Harriet along with numerous supporting parts in movies and also appeared in television commercials for (among other products) Shasta Grape Soda. Cady has been most prolific in television and was the only actor to play a recurring character on three TV sitcoms at the same time, The Beverly Hillbillies, Green Acres and Petticoat Junction, from 1968 to 1969. He also was one of only three co-stars of Petticoat Junction who stayed with the series for its entire seven-year run along with Edgar Buchanan and Linda Henning, appearing in 170 of the show's 222 episodes.

Cady married his wife Shirley in 1940. Shirley, born Shirley Katherine Jones, died August 22, 2008, at the age of 91.

They have two children, three grandchildren, and three great-grandchildren.

Maverick