LONDON — Shirley Williams, a pioneering British lawmaker and former cabinet member who broke from the Labour Party in the 1980s to help found a centrist movement that briefly promised to upend British politics, died on Monday at her home in England. She was 90.
Her death was announced by one of the parties she had helped establish, the Liberal Democrats. No other details were provided.
Charismatic and principled, Ms. Williams was long a force in British politics, serving in senior positions in a male-dominated Parliament and rising to cabinet ministerial posts. Many lawmakers have cited her career as an inspiration. Mark Peel, author of “Shirley Williams: The Biography,” said in an interview, “She gave politics a very good name.”
In 1981, concerned that the Labour Party was veering too far to the left, Ms. Williams and three other senior Labour lawmakers, known as the Gang of Four, founded the more centrist Social Democratic Party. It then formed an alliance with the old centrist Liberal Party and attracted a surge of support.
But Britain’s victory in the 1982 Falklands War revived the popularity of Margaret Thatcher’s Conservative government, and the 1983 general election proved a disaster for the left and center-left. The alliance won a quarter of the vote nationwide, a little less than Labour’s second-place showing, but far fewer seats than Labour.
The split among the opposition helped hand the Thatcher government a landslide majority in Parliament and cemented a Conservative political dominance that would last into the next decade.
The Social Democrats and the Liberals joined forces again in 1988 to form the Liberal Democrats, a centrist, socially progressive, pro-European party; Ms. Williams was a strong supporter of Britain’s entry into what was then known as the European Economic Community, a forerunner of the European Union. The Liberal Democrats grew to count more than 120,000 members.
She was born Shirley Vivian Teresa Brittain Catlin on July 27, 1930, joining a vibrantly political household in London. She was the daughter of Vera Brittain, a pacifist, feminist and wartime nurse whose searing memoir of World War I, “Testament of Youth,” in which she described losing her fiancé, brother and two close male friends in the fighting, is widely considered a classic.
Ms. Williams’s father was George Catlin, a professor of political science who ran unsuccessfully for Parliament as a Labour candidate in the 1930s.
Enrolling at Oxford University, Ms. Williams set her eyes on politics early, becoming the first woman to chair the Labour Club there, in 1950. At Oxford she studied politics, economics and philosophy and acted in drama productions. She later won a Fulbright scholarship to study American trade unions at Columbia University.
Returning to Britain, she took up journalism, working for The Daily Mirror and The Financial Times. But she also kept her eyes on a political career, running unsuccessfully as a Labour candidate for Parliament in the 1950s before winning a seat in 1964, from the town of Hitchin, in southern England.
She quickly climbed the ranks, becoming minister for education and science in the Labour governments of Prime Minister Harold Wilson in the ’60s. After the 1970 general election, when Labour lost power, she served as Labour’s spokeswoman on home affairs. In subsequent Labour governments in the ’70s she served as a trade secretary and then secretary of education under Prime Minister James Callaghan.
But Labour in the late 1970s became divided over issues like Britain’s membership in the European Economic Community, unilateral nuclear disarmament and the political influence of trade unions. Left-wing party members criticized Ms. Williams, a centrist, for not doing enough to promote equality, and in the 1979 general election she lost her seat.
Mr. Peel, her biographer, said “it wasn’t just policy” that estranged her from the party; “it was about the atmosphere — the sense of intolerance.”
“That enraged her,” Mr. Peel said. Ms. Williams began referring to what she called the “fascist left,” he said.
She and the three other senior Labour members — Roy Jenkins, David Owen and Bill Rodgers — announced the formation of the centrist Social Democratic Party in January 1981.
“She was not somebody who liked taking orders from party whips or party machines,” Mr. Peel said. “She was in many ways a free spirit, an individual who did her own thing.”
At a time when few women had climbed to senior positions in politics, Ms. Williams faced extra challenges. She spoke in a 1979 interview about the difficulties of balancing domestic life with her parliamentary duties. Women, she observed, “have the business of trying to keep two lives going.”
She later said that the political demands on her time led in part to the annulment of her first marriage, to the philosopher Bernard Williams, whom she married in 1955 and with whom she had a daughter, Rebecca, her only immediate survivor. Mr. Williams died in 2003. Ms. Williams married the American historian and presidential adviser Richard E. Neustadt in 1987. He also died in 2003.
After forming the Social Democrats in 1981, Ms. Williams won the party’s first parliamentary seat that year, in Crosby, in northwestern England, taking it from the Conservatives. But she lost the seat in the disastrous 1983 general election.
After the Social Democrats merged with the Liberals to form the Liberal Democrats in 1988 — a union she helped engineer — Ms. Williams moved to the United States to teach at what is now the Harvard Kennedy School of government.
She returned to Britain in 1993 after being made a peer in the House of Lords, with the title Baroness Williams of Crosby. Though she held socially progressive views generally, as a Roman Catholic she opposed gay marriage and adoption by gay couples, though she approved of civil unions between gay people.
She retired from the House of Lords in 2016 but continued to encourage women to enter politics. She also spoke out against Britain’s leaving the European Union, lamenting the polarization that the “Brexit” issue had fomented. “I find that heartbreaking,” she said a 2019 Sky News interview.
In her final speech in the House of Lords, Ms. Williams reminded her colleagues that Britain had a tradition of leadership that was “not just national but global — where we are part of a larger group of human beings seeking a better world and a better life.”
“I think it would be a tragedy if the country gave up that kind of leadership,” she said.