Saint died of natural causes at her home in Los Angeles, a statement from her spokesperson said on Tuesday.
Saint won an Oscar in her film debut for her portrayal of the virtuous Edie Doyle in director Elia Kazan's gritty 1954 drama On The Waterfront, then changed direction as the spy Eve Kendall in director Alfred Hitchcock's 1959 thriller North By Northwest.
The New Jersey native worked with a procession of big-name directors and stars after honing her craft at the Actors Studio, Lee Strasberg's famed "method acting" school in New York.
Saint said her mentor was the great silent film actress Lillian Gish, who appeared with her in a 1953 production of the play The Trip To Bountiful that brought her to Kazan's attention. He picked Saint for On The Waterfront over Elizabeth Montgomery.
Saint was 30 at the time but was playing a schoolgirl.
The movie won eight Academy Awards, including best picture, with Kazan named best director, Brando best actor and Saint best supporting actress.
Saint was pregnant when she accepted her Oscar in March 1955. She gingerly walked to the stage, kissed the golden statuette and excitedly told the audience, "I may have the baby right here!" Two days after the ceremony, she gave birth to her first child, Darrell Hayden.
Saint was born on July 4 1924, in New Jersey. Her early career was spent in live television productions in the formative years of the medium. She married veteran TV director Jeffrey Hayden in 1951 - a marriage that lasted until his death in 2016 - and they had two children. She starred in about 20 movies but turned down many roles to devote time to her family.
Later in her career, Saint often returned to TV work. She won an Emmy Award in 1990 for her performance in the drama People Like Us.
She also took movie roles into her 80s including Because Of Winn-Dixie (2005), Winter's Tale (2014) and Superman Returns (2006), a film in which Brando appeared posthumously using 1970s archive footage.
