Born in Canton, Ohio, Garner's mother pushed her into the limelight, and entered her in talent quests while Garner was still a child. By 1938 she had made her first film appearance and over the next few years appeared in several more films including the young Jane in Jane Eyre (1944). She reached the height of her success at the age of 13 in A Tree Grows in Brooklyn (1945) winning an Academy Juvenile Award largely on the basis of this performance.

Like many child performers, Garner was unable to make a successful transition into adult roles, although she did receive several supporting roles in films during the early 1950s. After her film career ended, she ventured into stage acting and had some success, but also worked as a real estate agent between acting jobs in order to support herself. Her final screen performance was a small part in a made for television feature in 1980.

Garner died from pancreatic cancer.