Tony Benn, pictured in 1967, puffs on his pipe as he listens to speeches during the second day of the 66th annual Labour Party Conference, in Scarborough, England. (Laurence Harris/AP)

Tony Benn, a British socialist who irritated and fascinated Britons through a political career spanning more than five decades and who renounced his aristocratic title rather than leave the House of Commons, died March 14 at his home in London. He was 88.

His family announced the death but did not give a cause.

Mr. Benn held Cabinet posts in Labour Party governments in the 1970s and clung unswervingly to his leftist beliefs while his party, in opposition, moved to the center and reemerged to take power again as New Labour. The change left Mr. Benn out of step with his party’s new, younger leaders.

“New Labour’s prime object is to destroy old Labour,” Mr. Benn complained when Tony Blair led the party to a landslide victory in May 1997, ending a generation of Conservative Party rule. “But you can’t just wish away a movement, a history, with a sound bite. You just can’t do it.”

Mr. Benn, who favored abolition of the monarchy, British withdrawal from the European Union and any strike that was going, had not changed. But his image did. He was over time transformed from the demonized figure of the ’70s and ’80s to that often-treasured English archetype: the radical dissenter.

“He had this wonderful vision of the working class,” former left-wing Labour lawmaker Joe Ashton recalled in a 1995 BBC television documentary. “It was almost like the Noble Savage, and sometimes we had to bring him down to earth.”

Anthony Wedgwood Benn was born in London on April 3, 1925, and was the second son of William Wedgwood Benn, a Labour Cabinet minister, and the former Margaret Holmes, a scholar in Greek and Hebrew studies. One grandfather was a baronet, and both had been members of Parliament.

He was educated at Westminster, an expensive private school, and the University of Oxford, where he was president of the Union, the university’s prestigious debating society.

In 1944, his elder brother, Michael, was killed in World War II, making Tony Benn the reluctant heir to the title Viscount Stansgate, which George VI had bestowed on his father in 1941.

He was elected to the House of Commons at 25, but his parliamentary career seemed to come to an abrupt end when his father died in 1960. As the new Viscount Stansgate, he was barred from the Commons so that he could take up membership in the unelected upper House of Lords.

For three years, he battled to change the law to allow hereditary peers to renounce their titles. Voters in his parliamentary district of Bristol West elected him once more, even though he could not take his seat in the Commons.

In 1963, the bill passed, and the Times of London declared, “Lord Stansgate will be Mr. Benn today.”

Labour Prime Minister Harold Wilson made Mr. Benn the industry secretary in 1974 but moved him to energy secretary a year later — a job where his left-wing, pro-union activities were less noticeable.

He lost his parliamentary seat in 1983 when the Conservatives’ Margaret Thatcher inflicted her most devastating defeat on Labour. A year later he was back, returned in a special election for Chesterfield, a depressed northern England former coal-mining district.

Through decades, Mr. Benn, a notable orator with a slight lisp, preached in chilly town halls, on the hustings and in the Commons. He had a single theme: socialism and the cause of “working people and their families.”

No setback ever seemed to depress him — not five failed attempts to become Labour leader or deputy leader, not getting dumped from the party hierarchy in the ’80s, not the emasculation of the labor unions by Thatcher, not Labour’s transformation, not the personal criticism.

“The five lines about me are: you’re an aristocrat, you’re a multimillionaire, you’re a hypocrite, you’re mad, you’re ill,” Mr. Benn said in a 1994 newspaper interview. “It took me a while to realize that their purpose was to discourage people from listening to what I am saying.”

Mr. Benn retired from the House of Commons in May 2001, after 51 years in Parliament, to “devote more time to politics.” By then he was the longest serving Labour MP in the history of the party, which he joined in 1942.

If anything, Mr. Benn lived more in the limelight after he retired from the House. He became a regular broadcaster, and his 2002-03 speaking tours of Britain titled “An Audience with Tony Benn” never failed to sell out.

He was extremely outspoken in his opposition to the 2003 war in Iraq, and days before the final commencement of hostilities, he traveled to Iraq to interview Saddam Hussein.

He was married to Caroline Middleton de Camp, a member of a well-off Cincinnati family, from 1949 until her death in 2000. They had three sons — Stephen, Joshua and Hilary, who is a Labour member of Parliament and ran for the deputy leadership of the party in 2007 — and a daughter, Melissa

— Associated Press