She returned to MGM for a role in The Singing Nun (1966) starring Debbie Reynolds. Her last film appearance was in the 1967 feature, Walt Disney's The Happiest Millionaire, although she made infrequent television appearances afterwards. In 1968, she narrated the children's television special The Little Drummer Boy. Her final role for television was in a 1982 episode of The Love Boat.
In 1967, the couple retired to their Forked Lightning Ranch in New Mexico. They purchased the US Hall of Fame champion Thoroughbred Ack Ack from the estate of Harry F. Guggenheim in 1971 and were successful as breeders. They also maintained a home in Dallas, where Garson funded the Greer Garson Theatre facility at Southern Methodist University. She founded a permanent endowment for the Fogelson Honors Forum at Texas Christian University (TCU), Buddy Fogelson's alma mater, in nearby Fort Worth.