Routinely described as one of her generation's finest actors, Ms. Thompson did not gain stardom until she was in her 40s, and was fixed in the public imagination as somebody's mother—often wise and noble, sometimes selfish and terrible, but always a figure of age and experience. Her breakout performance was in the original, 1970 staging of Paul Zindel's The Effect of Gamma Rays on Man-in-the-Moon Marigolds, in which she played the self-involved, unpleasant, slatternly mother of two very different children. "Sada Thompson does ample justice to both the ugliness and the remounts of humanity in Beatrice's character," wrote critic John Simon, "and manages the comic undertones as securely as the overtones of metaphysical horror."

She earned a Drama Desk Award and an Obie for her work in the Zindel play. Two years later, she won her Tony Award, as well as another Drama Desk Award, for Twigs, a group of four short plays by George Furth. In it she portrayed three different daughters as well as their mother. Other notable early performances include the horrendous Mommy in Edward Albee's early, cuttingly absurdist one-act American Dream, and the winsome, hopeful, doomed Winnie in Samuel Beckett's Happy Days.

But her matronly image derived for the most part from "Family," the 1970s landmark drama in which she starred alongside James Broderick, Meredith Baxter Birney and Kristy McNichol. She was Emmy-nominated four times for her performance as Kate Lawrence, the calm, dignified head of family who's everyday troubles were handled with an unusual amount of delicacy and seriousness. The show was applauded for dealing with issues—marital strife, homosexuality, divorce, infidelity—that were either taboo or ignored by other shows. Ms. Thompson won an Emmy for "Family" in 1978. She was also nominated for Emmys for her Mary Todd Lincoln in "Lincoln" (1976); Jack Lemmon's wife in "The Entertainer" (1976); "Our Town" (1978); "Cheers," in which she played Rhea Perlman's mother (1991); and "Indictment: The McMartin Trial" (1995).

Her Broadway debut was in The Carefree Tree in 1959, followed closely by the musical Juno. She played Dorine in a 1965 Lincoln Center revival of Moliere's Tartuffe, directed by William Ball. Following Twigs, she returned to Broadway in 1974 for Saturday Sunday Monday and then in 1993 for Any Given Day. Both productions only lasted a few weeks. In 1988, she was nominated for a Joseph Jefferson Award for Actress in a Principal Role in a Play for Driving Miss Daisy in Chicago.

She married Donald Stewart in 1949. He survives her, as well as a daughter.