Blyth began her acting career initially as “Anne Blyth”, but changed the spelling of her first name back to “Ann” at the beginning of her film career. She made her film debut in 1944, teamed with Donald O’Connor and Peggy Ryan in the teen-age musical Chip Off the Old Block (1944).

In April 1949, Universal suspended her for refusing a lead role in Abandoned (1949). Gale Storm played it.

MGM had been interested in Blyth since The Great Caruso. In December 1953, Blyth left Universal and she signed a long-term contract with MGM.

In 1953, Blyth married obstetrician James McNulty, brother of singer Dennis Day, who had introduced them. The bridesmaids were actresses Joan Leslie, Jane Withers, and Betty Lynn. The couple received special commendation from the Pope.

In 1955, an armed man who had written her fan letters was arrested near her house.

In 1957, she sued Benedict Bogeaus for $75,000 for not making the film Conquest.

From the late 1950s into the 1970s, Blyth worked in musical theater and summer stock, starring in the shows The King and I, The Sound of Music, and Show Boat. She also appeared sporadically on television, including co-starring opposite James Donald in the 1960 adaptation of A.J. Cronin’s novel, The Citadel.

In 1973, she and McNulty, both devout Catholics, were accorded the honorific rank of Lady and Knight of the Holy Sepulchre in a ceremony presided over by Terence Cardinal Cooke. McNulty died on May 13, 2007, in La Jolla, California.

Her last television appearances were in episodes of Switch and Quincy, M.E. in 1983 and Murder, She Wrote in 1985 (the year she officially retired).