The five-foot five Greer began life as Bettejane Greer in Washington, D.C., the daughter of Charles Durell McClellan Greer, Jr., and his wife, Bettie. In 1940, at age 15, Greer suffered from a facial palsy, which paralyzed the left side of her face. She recovered, but it has been speculated that the condition contributed to her "patented look" and "a calm, quizzical gaze and an enigmatic expression that would later lead RKO to promote her as 'the woman with the Mona Lisa smile'." She claimed that the facial exercises used to overcome the paralysis taught her how to convey human emotion.

Howard Hughes spotted Greer modeling in the June 8, 1942, issue of Life magazine and sent her to Hollywood to become an Actress. Hughes lent out the Actress to RKO to star in many films, (another source says Greer's then-husband, Rudy Vallee, "helped her get out of her contract with Hughes and secure another pact with RKO Studios") including Dick Tracy (1945), Out of the Past (1947), They Won't Believe Me (1947), and the comedy/suspense film The Big Steal (1949), alongside Out of the Past co-star Robert Mitchum. Hughes refused to let her work for a time; when she finally began film acting again, she appeared in You're in the Navy Now (1951), The Prisoner of Zenda (1952), Run for the Sun (1956), and Man of a Thousand Faces (1957). In 1984, she was cast in Against All Odds, a remake of Out of the Past, as the mother of the character she had played in 1947.

Jane Greer married Rudy Vallee on December 2, 1943, in Hollywood. They separated after three months and divorced on July 27, 1944. On August 20, 1947, Greer married Edward Lasker (1912–1997), a Los Angeles Lawyer and businessman, with whom she had three sons: Alex, Steven, and Lawrence, a movie Producer (WarGames, Sneakers). Greer and Lasker divorced in 1967. Frank London (an actor and dialogue coach) was Greer's domestic partner from 1965 until his death in 2001; he predeceased her by six months.

On December 4, 1945, Greer had her name legally changed to Jane Greer by a court in Los Angeles. She said of her previous name: "Mine is a sissy name. It's too bo-peepish, ingenueish, for the type of role I've been playing. It's like Mary Lou or Mary Ann."

In 1952, Greer obtained a release from her contract with Metro-Goldwyn-Mayer Studios. She said: "When there is a good role at MGM, the producers want Lana or Ava. There is no chance for another Actress to develop into important stardom at the studio."

Greer was honored with a star on the Hollywood Walk of Fame at 1634 Vine Street for her contributions to the motion picture industry. The star was dedicated on February 8, 1960.

Greer's noteworthy roles in television included guest appearances on episodes of numerous shows over the decades, such as Alfred Hitchcock Presents, Bonanza, Quincy, M.E., Murder, She Wrote, and a 1975 gig with Peter Falk and Robert Vaughn in an episode of Columbo titled Troubled Waters. She even got to make fun of Out of the Past in a parody with Robert Mitchum on TV's Saturday Night Live in 1987. Greer joined the casts of Falcon Crest in 1984, and Twin Peaks in 1990, in recurring roles.

Greer died of cancer on August 24, 2001 at the age of 76, in Bel Air, Los Angeles. Her body was interred at Los Angeles' Westwood Village Memorial Park Cemetery.