Judy Lewis is the biological daughter of actress Loretta Young and actor Clark Gable, who had an affair while working on the film Call of the Wild. Young concealed her pregnancy to protect her own and the Gable's film careers. After leaving Judy in an orphanage for some months, she returned to "adopt" her. When Judy was four years old her mother married businessman Tom Lewis and she went by the last name of Lewis. However Tom never adopted Judy, because he never knew that she was his wife's biological daughter, a fact he would have found out if he adopted her. She is the niece of actresses Polly Ann Young, Sally Blane, and Georgiana Young. Her Aunt Georgiana Young, Loretta Young's half-sister, was married to actor Ricardo Montalbán until their deaths. She is also the half-sister of John Clark Gable, Christopher Lewis and Peter Lewis. Musician David Lindley is her cousin.

Lewis' credits include appearances on TV soap operas such as General Hospital, Kitty Foyle, Days of our Lives and The Secret Storm. She also produced the short-lived Another World spin-off, Texas and was a script writer for NBC Daytime's Search for Tomorrow.

In 1958, Lewis guest starred in the episode entitled "Attack" of the syndicated western series Mackenzie's Raiders, starring Richard Carlson. In 1960, she guest starred as a girlfriend of a U.S. Navy officer in the episode "Tiger Blood" of the syndicated series The Blue Angels. In the 1961-1962 television season, she appeared as Connie Masters, an employee of the Wells Fargo office in Stillwater, Oklahoma, in the NBC western television series The Outlaws.

Lewis is divorced with one daughter, Maria, and two grandsons. She is a practicing psychotherapist in Los Angeles, California.