Mary Healy was born on April 14, 1918, in New Orleans, Louisiana. Crowned Miss New Orleans in 1935, Healy performed as a singer in the New Orleans area. She made her first screen appearance in Josette (1938). In 1939 she had major film roles in Second Fiddle and Star Dust, in which she sang the title song.

That year she also met entertainer Peter Lind Hayes, who was performing in North Hollywood with his mother, vaudevillian Grace Hayes. Healy and Hayes were married from 1940 until his death in 1998. With few exceptions she and her husband worked together exclusively.

Healy made her stage debut in Count Me In (1942), opposite Charles Butterworth and Jean Arthur. She starred as Mrs. Aouda in Orson Welles's 1946 Broadway production of Around the World in 80 Days, a role that she later reprised for The Mercury Summer Theatre on the Air radio adaptation of the musical play.

Healy was a member of the regular cast of Hayes's CBS-TV series, Inside U.S.A. with Chevrolet (1949–50), a revue-style series that Producer Arthur Schwartz based on his successful Broadway show, Inside U.S.A. Healy and Hayes were the first to sing the commercial jingle, "See the USA in Your Chevrolet", which later became a signature song for Dinah Shore.

Among the couple's other joint ventures on television were The Stork Club (1950), a CBS interview program; NBC's The Peter Lind Hayes Show (1950–51), a live situation comedy in which they played themselves on a set matching their actual New Rochelle home; the second season of the CBS variety show, Star of the Family (1951–1952); and the NBC sitcom Peter Loves Mary (1960–61), in which they played a show Business couple with two children who are adjusting to suburban life. Healy and Hayes were among the substitute hosts of The Tonight Show in 1962, between Jack Paar's departure and Johnny Carson's arrival, and they were regular substitute hosts on Arthur Godfrey's TV programs. They were frequent guest panelists and once were the mystery guests on the long-running quiz show What's My Line? The couple were also Celebrity contestants on the TV game show Password.

Healy and Hayes appeared in the cult fantasy film The 5,000 Fingers of Dr. T (1953) and the Broadway comedy Who Was That Lady I Saw You With? (1958), written by Norman Krasna.

During the 1960s they starred in a breakfast conversation show on New York radio station 710 WOR. WOR set up equipment in their house in suburban New Rochelle, New York so that they could broadcast on weekday mornings from their home.

Over the years Healy and Hayes headlined on 14 occasions at the Sands Hotel in Las Vegas. The couple published a memoir, Twenty-Five Minutes from Broadway, in 1961. Healy self-published a second book, Moments to Remember with Peter and Mary — Our Life in Show Business from Vaudeville to Video, in 2004. In 2006 she was inducted into the Nevada Entertainment/Artist Hall of Fame at the University of Nevada, Las Vegas.

Healy and Hayes were the parents of two adopted children – a son, Peter Michael Hayes, and a daughter, Actress Cathy Lind Hayes. Healy died of natural causes February 3, 2015, in Calabasas, California, aged 96.