The death was announced by her agent, Lionel Larner, who did not provide a specific cause.

Ms. Jackson was regarded as one of the leading screen and stage talents of her generation. As a young woman in the 1960s and ’70s, she drew attention for pushing cinematic boundaries in her portrayals of fiercely independent, even abrasive, female characters, many of whom explore their sexual freedoms.

Decades later — after 24 years in politics — she tackled stage roles confronting mortality and grief, including “King Lear” in 2016 in London and on Broadway with a Tony Award-winning performance as the aged, death-defying character called A in Edward Albee’s “Three Tall Women” in 2018.

She never wore her fame lightly, however. Ms. Jackson could be defensive and dismissive in interviews, troublesome with other actors and directors, and carried herself with a gruff defiance. She chain-smoked, flung around curse words like confetti and treated acting the way a rodeo cowboy treats a steer. It was something to be chased, roped and brought under control. Acting, she said, was hard work. And that requires sacrifice and focus.

“I regard acting,” she once said, “as a serious job for serious-minded people.”

As a teenager from a working-class background, Ms. Jackson joined an amateur acting troupe on a lark while working at a pharmacy near her hometown outside Liverpool. It led to a scholarship to the Royal Academy of Dramatic Art in London, the steppingstone for Britain’s elite of stage and screen. Yet Ms. Jackson said she was self-conscious about her looks, including eyes that compress into a piercing gaze.

The academy’s principal said she was destined to be nothing more than a middle-aged character actress, she recalled. Ms. Jackson took it as a lifelong challenge. She always seemed to be trying to set her own agenda on her own timetable.

In the 1960s and early 1970s, Ms. Jackson brought a mix of neurosis and eroticism to a series of roles, including the sex-obsessed wife in Ken Russell’s biopic on Russian composer Pyotr Ilyich Tchaikovsky, “The Music Lovers” (1971), and as the French Revolution assassin Charlotte Corday in Peter Brook’s production of “Marat/Sade” (1967). For a time, she was dubbed “the first lady of the flesh” of British cinema.

After her first Oscar nomination — as the cursed Gudrun Brangwen in Russell’s 1969 “Women in Love,” based on the D.H. Lawrence novel — Ms. Jackson was not on hand at the Academy Awards ceremony when her name was read out as the winner for best actress. She said she was “busy,” but the rebuff was widely interpreted as a personal stand against Hollywood’s glitz and vanities.

She also stayed away for her second Oscar in the 1973 romantic comedy “A Touch of Class,” playing opposite George Segal as a couple having a deepening affair. She received two more Academy Award nominations: as part of a love triangle with gay and bisexual men in “Sunday Bloody Sunday” (1971) and for 1975’s “Hedda,” an adaptation of Henrik Ibsen’s “Hedda Gabler,” about a manipulative woman.

By the early 1990s, after a mediocre run of cinema roles, she put acting aside and won a seat in Parliament representing north London for the Labour Party. “The best theater is trying to tell the truth,” she said. “And the best politics is trying to tell the truth.” For Ms. Jackson, who raged against conservative Prime Minister Margaret Thatcher, getting into politics was a chance for payback.

Ms. Jackson stayed in the House of Commons until 2015, including two years as a junior transport minister in the late 1990s in Prime Minister Tony Blair’s government. She left the Cabinet to make an unsuccessful run for London mayor and later slammed Blair for sending British forces into the U.S.-led war in Iraq in 2003.

At age 79, she decided she was running out of steam for politics. Acting, she said, turned out to be easier in some ways. She missed the ensemble. “The responsibility in acting is not exclusively mine,” she told the Guardian. “There’s a shared responsibility.”

She picked Shakespeare for her return. She watched her friend, actress Núria Espert, take on the role of King Lear in Spain. Ms. Jackson marveled at how well a woman could pull it off. Espert suggested Ms. Jackson do the same. “Don’t be absurd,” Ms. Jackson replied.

“Then other people said to me: ‘If you’re going to come back, come back with something.’ … So I said, ‘I’ll either crash and burn or whatever,’” Ms. Jackson recalled.

“King Lear” opened at London’s Old Vic in 2016. (It premiered on Broadway in 2019.) New York Times drama critic Ben Brantley judged it a “powerful and deeply perceptive performance as the most royally demented of Shakespeare’s monarchs.”

Glenda May Jackson was born in Birkenhead, near Liverpool, on May 9, 1936. Her father was a bricklayer, and her mother was a house cleaner and worked at a pub. The family moved to nearby Hoylake and struggled to make ends meet after her father was called to military service in World War II.

“We used to eat candle wax as an alternative to chewing gum,” she recalled.

Ms. Jackson left school at 15 and found a job at the chain pharmacy Boots. On a whim, she signed up for a local theater group. In 1954, she received a scholarship at the Royal Academy of Dramatic Art and made her professional debut in London in a production of Terrence Rattigan’s “Separate Tables” in 1957.

Six years later, she received her first big break. Brook picked her for an experimental troupe within the Royal Shakespeare Company. She made her mark with a burning intensity, leading to her being cast in “Marat/Sade.”

That same passion also became a red flag for other actors and directors. Ms. Jackson was soon labeled as someone who needed a wide berth. She berated other actors she felt were not carrying their weight and challenged directors over how they envisioned a scene. A co-star in “Women in Love” and two other films, Oliver Reed, described working with Ms. Jackson as “being run over by a Bedford truck.”

In a 1989 Los Angeles production of “Who’s Afraid of Virginia Woolf?” directed by the playwright Albee, Ms. Jackson even bickered with him over stage directions for her character, Martha. “He is a very, very good writer,” she later said. “Terrible director in my opinion.”

At the same time, she was also seen as a performer who could, at her best, elevate any role and bring her castmates along. In 1971, she helped infuse a raw power to a BBC television miniseries, “Elizabeth R,” about the 16th century reign of Elizabeth I. For the part, which earned Ms. Jackson an Emmy Award and aired on public television in the United States, she learned archery and calligraphy and shaved her head as the queen progressed from youth to old age.

In “Stevie” (1978), she won multiple film critic awards, playing the British poet Stevie Smith, and received an Emmy nomination for her 1981 TV movie, “The Patricia Neal Story,” about the Hollywood actress after several strokes left her incapacitated.

In 1985, she earned a Tony nomination for her role as Nina Leeds, the central character in Eugene O’Neill’s four-hour melodrama “Strange Interlude.”

When Ms. Jackson fell short, however, the reviews could be scathing. “Dirty Habits,” a 1977 Watergate-style scandal retold in a convent and starring Ms. Jackson, was blasted by film critic John Simon as an “ugly, unfunny travesty.” In 1978, Variety wrote that Ms. Jackson’s performance in the rom-com “House Calls” with Walter Matthau “would certainly suggest that comedy is not her bag.” The film did well at the box office and brought unusually glowing praise from Ms. Jackson about Matthau.

“Oh, God, did I enjoy working him!” she said in a 2018 interview with the Hollywood Reporter. She teamed up again with Matthau in “Hopscotch” (1980), about a CIA retiree on the run from his former agency.

She recently completed filming “The Great Escaper,” co-starring Michael Caine as a World War II veteran who slips away from his care home to attend the 70th anniversary commemoration of the D-Day landings.

Ms. Jackson’s marriage to Roy Hodges, an actor and stage manager, ended in divorce. Survivors include their son, journalist Dan Hodges. Ms. Jackson remained single, saying that “men are awfully hard work for very little reward.”

“When I have to cry,” she later said, “I think about my love life. And when I have to laugh, I think about my love life.”

While Ms. Jackson described herself as a performer deeply rooted in Britain, one classic British role was turned down. She was offered a chance to play M, the intelligence chief, in the James Bond series — a role that went to Judi Dench. No regrets, Ms. Jackson said. She rejected the M role “because it was boring.”

“That is one of the really shocking things that hasn’t changed in my 25 years of being out of it,” she told the Guardian in 2016 after returning to acting. “Creative writers still don’t find women interesting. They are hardly ever the dramatic engine, they are mostly an adjunct, and I find that very bizarre.”