Born in Jamesport, Missouri, Scott earned a degree in drama from the University of Michigan in 1934. After playing Shakespearean roles at the 1933-34 Chicago World's Fair, she came to New York to pursue her career. Following the dismissal of another actress, she landed the plum role of Emily in Our Town (1938), playing it opposite George Craven on stage and opposite William Holden in the 1940 movie. (Though the film had a cast including Fay Bainter, Beulah Bondi, and Thomas Mitchell, and though it featured a score by Aaron Copland, it suffered from a rewritten happy ending in which Emily does not die in childbirth. Largely for that reason, the movie is not held in high esteem and has apparently been in the public domain for years.)
Scott's other film credits include The Howards of Virginia, with Cary Grant, In Old Oklahoma with John Wayne, and The Desperate Hours with Humphrey Bogart. Most famously, she played Charlton Heston's mother in two enormously popular films -- The Ten Commandments and Ben-Hur -- even though she was only about 10 years older than he. She also played Heston's wife on Broadway in The Tumbler (1960). Among her other Broadway shows were Foreigners (1939), The Male Animal (1952), The Remarkable Mr. Pennypacker (1953), The Subject Was Roses (as a replacement in 1964), and 1975 revival of Thornton Wilder's The Skin of Our Teeth.
In 1968, in partnership with fellow actors Henry Fonda and Robert Ryan, Scott founded a theatrical production company called the Plumstead Playhouse in New York. The organization presented revivals of several classic plays with all-star casts before relocating to Los Angeles and changing its name to the Plumstead Theatre Company. Scott also co-produced the Broadway show First Monday in October (starring Fonda and Jane Alexander) as well as the movie version (starring Walter Matthau and Jill Clayburgh). In 1985, she was a producer of a Los Angeles staging of Twelve Angry Men.
In her later years, Scott made several television appearances; most notably, she played Sue Ellen Ewing's mother on the nighttime soap opera Dallas and also had a recurring role in the daytime soap opera General Hospital. Her last Broadway role came in 1991, when she played Rebecca Nurse in The Crucible -- the inaugural production of the National Actors' Theatre, established by Tony Randall.
Scott's first marriage to Carlton Alsop, a radio and film producer, ended in divorce in 1946. She later married composer Mel Powell, who died in 1998. Scott is survived by a son, Scott Alsop; two daughters, Mary Powell Harpel and Kathleen Powell; and a brother, Charles Scott. According to The New York Times, Scott asked to be buried in the cemetery in Jamesport, where she rehearsed Emily's graveyard scene.