The Rev. Ian Paisley, Northern Ireland’s firebrand Protestant leader, who vowed never to compromise with Irish Catholic nationalists, then, in his twilight, accepted a power-sharing agreement that envisioned a new era of peace in Northern Ireland after decades of sectarian violence, died on Friday in Belfast. He was 88.

In failing health in recent years, Mr. Paisley had been fitted with a pacemaker in 2011 after falling ill in London and had retired from politics and the pulpit. His wife, Eileen, confirmed his death in a statement.

The day many thought would never come arrived in Belfast on May 8, 2007. Mr. Paisley, founder of the Democratic Unionist party, which sought continued association with Britain, and Martin McGuinness, a Sinn Fein leader and former commander of the Irish Republican Army, which had fought for a united Ireland, took oaths as the leader and deputy leader, respectively, of Northern Ireland’s power-sharing government.

As Prime Ministers Tony Blair of Britain and Bertie Ahern of Ireland looked on, the proceedings ended direct British governance and reinstated home rule in Belfast. The agreement bridged the chasm between Mr. Paisley and Gerry Adams, the Sinn Fein leader who had negotiated it. And it relegated to the past the civil strife, known as the Troubles, that had raged from the 1960s into the ’90s and cost 3,700 lives.

The next year, Mr. Paisley — white-haired, 82 and seemingly mellowed — resigned as Northern Ireland’s first minister and as leader of the Democratic Unionists, by then the dominant party of Ulster’s Protestants, which he founded in 1971. He had already stepped down as head of the Free Presbyterian Church, which he founded in 1951, and had given up the seat he had held for 28 years in the European Parliament in Strasbourg, France. In 2010 he gave up the seat in the British House of Commons that he had held for 40 years.

It was the winding down of a tumultuous career as a rabble-rousing minister-politician whose single-minded objective had been to preserve Protestant power and repress the Roman Catholic minority in Northern Ireland, keeping Ulster aligned with Britain, across the Irish Sea, and out of the reach — he would have said the clutches — of predominantly Catholic Ireland to the south.

From the 1950s, when he organized vigilante patrols to defend Protestant neighborhoods against I.R.A. attacks, through decades of deadly turmoil — bombings, assassinations, clashes with British troops and general strikes and riots he had fomented — Mr. Paisley barnstormed the province, condemning any peace deal that might open the way to power-sharing with Catholics in Northern Ireland, which has nearly 1.8 million people.

In the pulpit or at Stormont — the Northern Ireland Parliament, which had been emblematic of Protestant hegemony since the partition of Ireland in 1921 — Mr. Paisley was a spellbinding orator, a thundering Jeremiah of relentless political attacks laced with biblical references. The Catholic Church, Sinn Fein, the I.R.A., Irish leaders, even interfering American presidents were all targets of the Paisley wrath.

He called Pope John Paul II the Antichrist. He said he wanted to kick Bill Clinton in the pants for his peace efforts. He refused to attend negotiations and accused some British leaders of plotting to sell Belfast out to what he called the devils in Dublin. His demands for the removal of an Irish flag from Sinn Fein’s Belfast office once led to two days of rioting. And he said “no” to almost everything — to civil rights for Catholics, to meetings with Irish leaders, and especially to power-sharing proposals.

John Hume, a Catholic civil rights leader, once said to Mr. Paisley, “Ian, if the word ‘no’ were to be removed from the English language, you’d be speechless, wouldn’t you?”

“No, I wouldn’t,” Mr. Paisley shot back.

While supporters called him a passionate defender of Protestant unionism, some said his negative stances alienated allies, prolonged violence and held back progress even as prosperity spread in the Irish Republic. Critics called him a bigoted demagogue who offered simple nostrums to complicated religious, cultural and social problems. But Mr. Paisley conceded nothing and denied culpability for any violence.

In 1998, a peace agreement was signed by David Trimble, the mainstream Ulster Protestant leader, and Mr. Hume, and they shared the Nobel Peace Prize that year for their efforts. The so-called Good Friday Agreement, ratified by voters in Ireland and Northern Ireland, was hardly radical. It provided that Ireland could be united only with the consent of Northern Ireland and made it likely that Northern Ireland would remain Protestant in perpetuity or at least well into the 21st century. But it envisioned power-sharing, and Mr. Paisley fulminated against it.

By 2007, however, a series of hurdles had been passed: The I.R.A. had destroyed its arsenal of weapons and dismantled its clandestine cells, and Sinn Fein had endorsed a reconstituted Northern Ireland police force, which it had long considered an arm of British and Protestant repression, leading Mr. Paisley to accept a power-sharing compromise reached at St. Andrews, Scotland.

On the day of his swearing-in as first minister in Belfast, a thriving city that had once been an armed fortress, Mr. Paisley was solemn. “While this is a sad day for all the innocent victims of the Troubles, yet it is a special day because we are making a new beginning,” he said. “I believe we are starting on a road to bring us back to peace and prosperity.”

Ian Richard Kyle Paisley was born on April 6, 1926, in Armagh, Northern Ireland. His father, James, was a Baptist minister; his mother, Isobel, a Scottish evangelist.

Raised in Ballymena, County Antrim, Ian attended local schools and worked on a farm. He decided to be a minister, studied at a South Wales evangelism school, graduated from Theological Hall of the Reformed Presbyterian Church in Belfast and was ordained in 1946.

But he soon came to believe that his church had deviated from biblical strictures, and he founded the Free Presbyterians, a relatively small fundamentalist sect. The Presbyterian Church, Northern Ireland’s largest Protestant denomination, disassociated itself from his anti-Catholic rhetoric.

In 1956, he married Eileen Cassells. The couple had three daughters, Sharon, Rhonda and Cherith, and twin sons, Kyle and Ian Jr. They all survive him, as do several grandchildren.

Mr. Paisley was 6-foot-4 and 240 pounds, with broad shoulders to go with a booming voice and a solemn demeanor. He was a teetotaler and nonsmoker who avoided movies and other entertainments he considered frivolous. But he was affable in a smoky bar with politicians drinking whiskey, which he called “the devil’s buttermilk,” and he sometimes told bawdy jokes.

Mr. Paisley wrote many volumes of religious and political commentaries, including “An Exposition of the Epistle to the Romans” (1968), “United Ireland — Never!” (1972), “America’s Debt to Ulster” (1976), “No Pope Here” (1982) and “The Protestant Reformation” (1999).

He was the subject of a documentary, “The Unquiet Man,” broadcast by the BBC in 2001, and a biography, “Paisley” (1986), by Ed Moloney and Andy Pollak. (A new edition, “Paisley: From Demagogue to Democrat?,” by Mr. Moloney, was published in 2008.)

After giving up the seat in the House of Commons that he had won in 1970, he was succeeded by his son Ian and was made a life peer in the House of Lords, as Baron Bannside of County Antrim. In January 2012, he retired after 65 years as the pastor of Martyrs’ Memorial Church in Belfast.

County Antrim, his ancestral home, was his political base. His Democratic Unionists, an outgrowth of the Protestant Unionists he founded, attracted wide followings but were not Ulster’s dominant Protestant party until 2005. His campaigns often featured fiery denunciations of homosexuality and what he called the blasphemies of popular culture.

But his politics were predominantly a crusade against Irish Catholics. And when it was over, when he had softened the diatribes and accepted leadership in a power-sharing government, the legacies of fighting and religious hatreds remained. Housing was still overwhelmingly segregated, discrimination in jobs was still common, and 3-year-olds, researchers said, continued to display sectarian instincts.