Wyatt died Friday in her sleep of natural causes at her Bel-Air home, according to publicist Meg McDonald. She experienced health problems since suffering a stroke at 85, but her mind was sharp until her death, her son said.
Wyatt had a successful film career in the 1930s and '40s, notably as Ronald Colman's lover in 1937's "Lost Horizon."
But it was her years as Robert Young's TV wife, Margaret Anderson, on "Father Knows Best" that brought the actress her lasting fame.
She appeared in 207 half-hour episodes from 1954 to 1960 and won three Emmys as best actress in a dramatic series in the years 1958 to 1960. The show began as a radio sitcom in 1949; it moved to television in 1954.
"Being a family show, we all had to stick around," she once said. "Even though each show was centered on one of the five members of the family, I always had to be there to deliver such lines as `Eat your dinner, dear,' or `How did you do in school today?' We got along fine, but after the first few years, it's really difficult to have to face the same people day after day."
The Anderson children were played by Elinor Donahue, Billy Gray and Lauren Chapin, and all grew up on the show. In later years critics claimed that shows like "Father Knows Best" and "Ozzie and Harriet" presented a glossy, unreal view of the American family.
In defense, Wyatt commented in 1966: "We tried to preserve the tradition that every show had something to say. The children were complicated personally, not just kids. We weren't just five Pollyannas."
It was a tribute to the popularity of the show that after its run ended, it continued in reruns on CBS and ABC for three years in primetime, a TV rarity. The show came to an end because Young, who had also played the father in the radio version, had enough. Wyatt remarked in 1965 that she was tired, too.
"The first year was pure joy," she said. "The second year was when the problems set in. We licked them, and the third year was smooth going. Fatigue began to set in during the fourth year. We got through the fifth year because we all thought it would be the last. The sixth? Pure hell."
The role wasn't the only time in her 60 years in films and TV that Wyatt was cast as the warm, compassionate wife and mother. She even played Mr. Spock's mom in the original "Star Trek" series and the feature "Star Trek IV: The Voyage Home."
She got her start in films in the mid-'30s, appearing in "One More River," "Great Expectations," "We're Only Human" and "The Luckiest Girl in the World." When Frank Capra chose her to play the Shangri-la beauty in "Lost Horizon," her reputation was made. Moviegoers were entranced by the scene — chaste by today's standards — in which Colman sees her swimming nude in a mountain lake.
Never a star, Wyatt enjoyed career longevity with her reliable portrayals of genteel, understanding women. Among the notable films:
"Buckskin Frontier" (with Richard Dix), "None But the Lonely Heart" (Cary Grant), "Boomerang" (Dana Andrews), "Gentleman's Agreement" (Gregory Peck), "Pitfall" (Dick Powell), "No Minor Vices" (Dana Andrews), "Canadian Pacific" (Randolph Scott), "My Blue Heaven" (Betty Grable, Dan Dailey) and "Criminal Lawyer" (Pat O'Brien).
"Father Knows Best" enjoyed such lasting popularity in reruns and people's memories that the cast returned years later for two reunion movies. She also remained active on other projects, such as "Amityville: The Horror Goes On" in 1989, and in charity work.
When Young died in 1998, Wyatt paid tribute to him as "simply one of the finest people to grace our industry."
"Though we never socialized off the set, we were together every day for six years, and during that time he never pulled rank (and) always treated his on-screen family with the same affection and courtesy he showed his loved ones in his private life," she said.
Wyatt was born in Campgaw, N.J., into a wealthy family in 1910, according to McDonald, her publicist. Her father, an investment banker, came from an old-line New York family, as did her mother, who wrote drama reviews. They gave their daughter a genteel upbringing, with her schooling at the fashionable Miss Chapin's school and Barnard College.
She left college after two years to apprentice at the Berkshire Playhouse in Stockbridge, Mass. For two years she alternated between Berkshire and Broadway, appearing with Charles Laughton, Louis Calhern and Osgood Perkins.
While acting with Lillian Gish in "Joyous Season" in 1934, she got a contract offer from Universal Pictures. She agreed, on condition she could spend half each year in the theater.
During college, Wyatt attended a party at Hyde Park, N.Y., given by the sons of Franklin D. Roosevelt. There she met a Harvard student, Edgar Ward. In 1935 she married Ward, then a businessman, in Santa Fe, N.M.
Ward is survived by sons Christopher, of Piedmont, California and Michael of Los Angeles; three grandchildren Nicholas, Andrew and Laura; and five great grandchildren.