Devry was born Thelma Elaine Mahnken to Fred P. and Hortense Mahnken in Compton, California, where she was raised. Her brother, Jeff, was three years her senior. She began to model at age fifteen. She graduated from Compton High School and later attended Compton Junior College, where she was homecoming queen.
After marrying her high school boyfriend, Dan Ducich, in 1948, the couple lived in Butte, Montana, until their 1952 divorce, upon which Devry returned to California, working as a carhop at the Dolores Drive-In on Wilshire Boulevard.
Devry appeared in a number of films including A Guide for the Married Man. She was formerly married to actor Mickey Rooney.
She was billed as Elaine Davis in her early acting roles, including her first film, The Atomic Kid, in which she and Rooney co-starred. Devry made three guest appearances on Perry Mason, including the title role of defendant Janice Wainwright in the 1962 episode, "The Case of the Shapely Shadow." She also appeared in many other popular television series, including Bonanza, 77 Sunset Strip, Burke's Law, Family Affair, I Dream of Jeannie and Marcus Welby, M.D..
Devry married Dan Ducich, her high school boyfriend, in Butte, Montana, in September 1948. The following year, Ducich was convicted of multiple robberies in Los Angeles and sentenced to five years probation. The couple resided in Butte, but divorced in 1952. She also had a six-year marriage to actor Mickey Rooney, whom she met in the fall of 1952, and married on November 15, 1952, in Las Vegas. They had a son, Jimmy, and a daughter, Jonelle.
As of 2005, Devry lived on a ranch in Oregon.