Madeleine Sherwood as Mother Superior in the 1960s sitcom “The Flying Nun.” (Everett Collection)

Madeleine Sherwood, a distinguished Canadian-born character actress who played saints and sinners on Broadway and TV — and who endured blacklisting in the 1950s and a prison term in the 1960s for her civil rights activism, died April 23 at her home in Saint-Hippolyte, Quebec. She was 93.

A family spokeswoman, Melissa Fitch, confirmed the death but did not disclose the cause.

While not a household name, Ms. Sherwood became a familiar pug-nosed face over a six-decade show-business career that included roles in landmark plays by Arthur Miller and Tennessee Williams and a singing part in a Stephen Sondheim-Richard Rodgers musical. She also portrayed the stern Mother Superior on the ABC sitcom “The Flying Nun” (1967-70), opposite Sally Field’s young and airborne novice.

Fields was ambitious to move beyond lightweight gamine roles, and she credited Ms. Sherwood, long affiliated with the Actors Studio theater workshop in New York, with getting her the training required for her transition into Oscar-winning dramatic parts in “Norma Rae” and “Places in the Heart.”

Ms. Sherwood’s own entry into acting had been tumultuous. An unhappy early marriage and postpartum depression landed her in an asylum, and she said her husband wanted her lobotomized. She told a friendly doctor that she simply wanted to be an actress, and he recommended she make an escape out the unlocked back door.

She set about reinventing herself, fueled by a raw talent for playing scheming and overbearing parts. She dazzled audiences and reviewers in Arthur Miller’s “The Crucible” (1953) as Abigail Williams, a spurned teenage hussy who spreads malicious accusations of witchcraft in 1692 Salem, Mass.

New York Times theater critic Brooks Atkinson praised her “fire and skill” in the powerful Miller morality play that many have read as an allegory against the McCarthyite anti-communist witch hunts of the day. (Ms. Sherwood said she was blacklisted for a period when she stood up for actress Lee Grant, who had been targeted by the House Un-American Activities Committee.)

In 1955, Ms. Sherwood had a notable supporting role on Broadway in Williams’s “Cat on a Hot Tin Roof,” about greedy relatives of a dying Mississippi plantation owner known as Big Daddy.

Playing a character often called Sister Woman, Ms. Sherwood tries to ingratiate herself by bearing a litter of Big Daddy’s grandchildren — a bunch of spoiled holy terrors memorably excoriated as “no-neck monsters.” Sister Woman is ultimately outfoxed by another daughter-in-law, Maggie the Cat, portrayed by Barbara Bel Geddes on stage and by Elizabeth Taylor in the 1958 movie version; Ms. Sherwood reprised her role for the film.

Ms. Sherwood played a key role in the 1959 Broadway and 1962 film adaptations of Williams’s “Sweet Bird of Youth” — as mistress of the malevolent Gulf Coast power broker Boss Finley. She suffers a cruel punishment for belittling her lover’s sexual impotence.

Ms. Sherwood continued her run of Southern-fried connivers in “Invitation to a March” (1960), a Broadway comedy written and directed by Arthur Laurents and featuring incidental music by Sondheim. It was a connection that led to her featured role on Broadway in “Do I Hear a Waltz?” (1965), the Sondheim-Rodgers musical in which she originated the part of Mrs. McIlhenny, an obnoxious American tourist.

Her other Broadway credits included the Alan Jay Lerner-Frederick Loewe musical “Camelot,” in which she replaced M’el Dowd as Morgan Le Fey in 1962. That same year, she briefly succeeded Bette Davis in Williams’s “The Night of the Iguana.” Her final Broadway appearance was in Edward Albee’s bleak and short-lived “All Over” (1971), directed by John Gielgud.

Ms. Sherwood won a 1963 Obie Award for distinguished performance in “Hey You, Light Man!,” Oliver Hailey’s wistful comedy about an actor in a play and his relationship with a member of the audience.

“There is simplicity and decency in this woman, who has always accepted the unadorned and unexciting realities of her ordinary life,” New York Times theater critic Howard Taubman wrote of Ms. Sherwood’s character. “Her transformation under the guidance of the actor into a person who can transcend reality is managed with admirable lightness and flexibility.”

Madeleine Louise Hélène Thornton was born in Montreal on Nov. 13, 1922. She won small roles with the Montreal Repertory Theatre but put aside her acting ambitions to marry Robert Sherwood (not the playwright of the same name), a union that ended in divorce. Survivors include a daughter, Chloe Fox, of Ontario; two grandchildren; and six great-grandchildren.

Ms. Sherwood was the longtime companion of the late Hylan Johnson, an actor known as “Dots” or “Dotts” and best remembered as a black American soldier in Roberto Rossellini’s 1946 film “Paisan.” She grew involved in civil rights causes and in May 1963 was arrested during a Freedom Walk in Etowah County, Ala. She was sentenced to six months of hard labor, but her lawyer, Fred D. Gray, said in an interview that the decision was “ultimately reversed” on appeal.

Later in life, Ms. Sherwood led acting workshops in which she passed on methods learned from mentors such as director Elia Kazan. Her teaching was the focus of a 2010 short film, “Madeleine’s Method.”

In the documentary, she also spoke of her thwarted ambitions for stardom and of the fleeting moments of triumph when she was center stage. When it was first announced that she would take over for Davis in “The Night of the Iguana,” she recalled, the audience began shifting in their seats, deciding whether to ask for a refund or stay.

Adopting the tough tone of her earthy and boozy character, she said, she walked from the stage into the audience and shouted at two restless ticket buyers: “ ‘You make up your mind. Either sit down or get out.’ . . . That broke the ice because the rest of the audience laughed. . . . From there on in, I sailed through.”