In 1934, at the age of sixteen, Lord made her Broadway debut in The Old Maid with Judith Anderson. The following year, she was signed with RKO Radio Pictures. While appearing in Springtime for Henry with Edward Everett Horton, director Henry Koster approached her and signed her to a contract with Universal Studios. She appeared in six feature films for Universal.

Her film work includes a number of wartime pictures, including the 1943 mystery Sherlock Holmes in Washington, starring Basil Rathbone in the title role. She appeared in the 1951 episode "The Return of Trigger Dawson" in Bill Williams's syndicated western television series The Adventures of Kit Carson.

In 1956, while she was appearing in Anniversary Waltz, Lord caught the attention of Danny Thomas, who asked her to replace Jean Hagen as his television wife on Make Room for Daddy. Hagen had played Thomas' wife since the series' inception, but she quit in 1956 and was written out of the script. Lord accepted, and played the role until the show was cancelled in 1964.

In 1970, Lord and Thomas, along with several original supporting actors, returned to television with Make Room for Granddaddy. The show lasted just one season.

Lord was born Marjorie F. Wollenberg in San Francisco, California. She has been married three times. Her first husband was actor John Archer, with whom she had two children, including actress Anne Archer. They were married from 1941 until their divorce in 1955. Her second husband was producer Randolph Hale, to whom she was married from 1958 until his death in 1974. Her third husband was banker Harry Volk, to whom she was married from 1976 until his death in 2000.

Lord has continued to remain active beyond her 90th birthday. On May 8, 2008, she participated in a "Salute to Television Moms" panel discussion organized by the Academy of Television Arts & Sciences.

Her memoir, A Dance and a Hug, is available on her website.