Senator Orrin G. Hatch, the Utah Republican who crusaded for right-wing causes and outlasted six presidents in a seven-term Senate career that corresponded to the rise of the conservative movement in America, died on Saturday in Salt Lake City. He was 88.

The Hatch Foundation confirmed his death in a statement. It did not specify a cause.

Born into poverty in the Great Depression, one of nine children of a Pittsburgh metal worker, Mr. Hatch, who briefly aspired to the presidency and to a seat on the Supreme Court, had a grim Dickensian childhood. He went to school in bib overalls, lost siblings in infancy and in World War II, and grew up in a crowded, ramshackle house without indoor plumbing.

In law school, he, his wife and children lived in a chicken coop that he and his father rebuilt behind his parents’ home.

“We turned it into a tiny two-room bungalow, with a toilet and small stove, that we nicknamed ‘the cottage,’ a description that would have made even the most aggressive real estate agent cringe,” he said in a memoir, “Square Peg: Confessions of a Citizen Senator” (2002).

But in the Senate, as in his early life, he was a fighter. Through shrewd political instincts and a fine-tuned sense of the national mood moving to the right, he became a powerful Washington political force, advising seven presidents, shaping some 12,000 pieces of legislation as a sponsor or co-sponsor, and helping to build and hold a conservative majority on the Supreme Court for years.

In a 42-year tenure that began weeks before Jimmy Carter became president in 1977 and ended as his last term drew to a close in early 2019, Mr. Hatch was one of the Senate’s best-known leaders, as familiar to many Americans as anyone on Capitol Hill. He conferred at the White House with Presidents Carter, Reagan, George Bush, Bill Clinton, George W. Bush, Barack Obama and Donald J. Trump, and voted to confirm nine justices of the Supreme Court.

He was the longest-serving Republican and the sixth longest-serving senator in the history of the Senate, a singular achievement made all the more remarkable by the fact that, aside from a run for the Republican presidential nomination in 2000, it was the only office he had ever sought. He was elected to the Senate in 1976 on his first try and re-elected six times by overwhelming margins. To make an orderly parting transition, he had announced nearly a year in advance that he would not seek an eighth term.

From January 2015, when the G.O.P. took control of the Senate, until his retirement, Mr. Hatch had been its president pro tempore — making him by law third in the line of succession to the presidency, after the vice president and the speaker of the House. It was just a whiff of presidential power, as those ambitions had long ago sputtered out.

By his final term, polls indicated that Utah voters believed it was time for Mr. Hatch to go. The Salt Lake Tribune facetiously named him “Utahn of the Year” in December 2017, and in an accompanying editorial had scathingly characterized his leading role in passage of the Trump tax cuts, which favored the rich, as an “utter lack of integrity.” The editorial reminded him of a 2012 promise not to run again in 2018.

Mr. Hatch’s departure notice, a courteous and politically astute move, was appreciated by many party colleagues because it cleared a way for former Massachusetts Gov. Mitt Romney, the 2012 Republican presidential nominee and a Mormon, to run for his seat.

Mr. Romney was easily elected in 2018 and succeeded Mr. Hatch when he stepped down. Republicans saw Mr. Romney as a strong addition to the Senate; Democrats knew he was no friend of Mr. Trump, whom he had derided as a “fraud” and “phony” during the 2016 campaign.

As the president pro tempore, Mr. Hatch was Mr. Trump’s designated successor during his Inaugural ceremonies — kept safe at an undisclosed location to ensure the government’s continuity, just in case. And in Mr. Trump’s first two years in office, he became one of the president’s most enthusiastic Senate loyalists, instrumental in achieving not only his tax cuts but the confirmation of his first two Supreme Court nominees, Neil M. Gorsuch and Brett Kavanaugh. In 2018, Mr. Trump conferred the Presidential Medal of Freedom, the nation’s highest civilian honor, on Mr. Hatch.

Throughout his Senate years, Mr. Hatch had been a gentlemanly, but relentless, conservative rock. He blocked labor law reforms and fair housing bills with filibusters, tying up Senate business for weeks. He voted against the Equal Rights Amendment, which would have enshrined gender equality as a bedrock civil right, and he proposed a Constitutional amendment to make abortion illegal.

In a chamber of party loyalties, Mr. Hatch was also fiercely independent and often unpredictable. A lifelong Mormon who had performed missionary work in his youth, he held hard-right views on gun control, capital punishment, immigration and balanced budgets. He also opposed same-sex marriage, although he endorsed civil unions and laws barring discrimination against gay and transgender people in housing and employment.

While he helped craft the court’s majority, he was hard to gauge on nominees. He voted for the conservatives Antonin Scalia (1986), Clarence Thomas (1991), John G. Roberts Jr. (chief justice, 2005), Samuel Alito (2006), Mr. Gorsuch (2017) and Mr. Kavanaugh (2018), and against the liberals Sonia Sotomayor (2009) and Elena Kagan (2010). But he also voted for Anthony Kennedy, a swing vote (1988) and for two liberals, Ruth Bader Ginsburg (1993) and Stephen Breyer (1994).

When politically expedient, Mr. Hatch edged toward the center. In 1990, after labeling Democrats “the party of homosexuals,” the senator, amid talk that he might be interested in a Supreme Court seat himself, retracted the disparagement. “That was a dumb thing to say,” he acknowledged. “That’s their business and I’m not going to judge them by my standards of what I think is right.”

Similarly, after his brief run for the Republican presidential nomination in 2000, he conceded the race to the eventual winner, George W. Bush, with centrist magnanimity. “I like the fact that he can reach across partisan lines,” Mr. Hatch said of Mr. Bush. “We can’t just take a narrow agenda and just narrowly be for a few people in this country. We’ve got to be for everybody.”

For all his conservative credentials, Mr. Hatch had a longstanding and genuine friendship with Senator Edward M. Kennedy of Massachusetts, the quintessential liberal Democrat. They spoke often and shared legislative accomplishments, including programs to assist AIDS patients, protect the disabled from discrimination and provide health insurance for the working poor. Mr. Hatch delivered a moving eulogy at Mr. Kennedy’s funeral in 2009.

The New York Times in 1981 described Mr. Hatch as “an aggressive, ambitious man who, as much as anything, resembles a minister making his rounds.” He was, in fact, a bishop of the Church of Jesus Christ of Latter-day Saints. Away from Capitol Hill, he led a quiet married life, the father of six children. He jogged, golfed and had an athlete’s trim look, even after his dark hair turned white.

Senators, even Republicans, called him relatively humorless. His idea of a good joke, on himself, was a video that caught him trying to remove glasses he was not wearing during a contentious Senate hearing. It went viral online. A spokesman said he laughed at himself when he saw it, and created a fake Warby Parker page implying that invisible glasses were the new rage.

Mr. Hatch had been an amateur boxer in his youth, with 11 bouts to his credit. He was also a pianist, a violinist and an organist, who wrote songs for pop groups and folk singers. In the early 1970s, he was the band manager for a Mormon-themed folk group, “Free Agency.” He also wrote books on politics and religion, and articles for periodicals and newspapers, including The Times.

He was 42 years old, a tall, slim Salt Lake City lawyer, when he went to Washington in 1977 after defeating a three-term Democratic incumbent with the help of an endorsement — for “Warren Hatch” — from Ronald Reagan. The former California governor lost his bid for the Republican presidential nomination to President Gerald Ford, but would sweep into office with his conservative revolution in 1980, counting Mr. Hatch as an ally.

As a Senate freshman, Mr. Hatch found mentors among its deepest conservatives — the Democrats James O. Eastland of Mississippi and Jim Allen of Alabama, and the Democrat-turned-Republican Strom Thurmond of South Carolina. He did not, however, share their ardor for racial segregation.

But he offered himself as a rising young protégé, and they taught him how to pass and block legislation, stage filibusters, build coalitions and horse-trade behind the scenes. In time, he became chairman of the Finance and Judiciary Committees, which wrote tax legislation and confirmed federal judges, and a power on committees that ruled the fate of health, education and labor bills.

His actions were consistently conservative: opposing Mr. Carter’s social welfare programs, favoring Reagan and Bush tax and spending cuts and fighting Clinton health care ideas. After the Sept. 11 terrorist attacks, he helped draft the USA Patriot Act and supported Mr. Bush’s retributive wars in Afghanistan and Iraq. He also opposed Mr. Obama’s Affordable Care Act, and backed Mr. Trump’s immigration initiatives and his withdrawal from the Paris accords on climate change.

Mr. Hatch was occasionally criticized for potential conflicts of interest. He publicly defended the Bank of Credit and Commerce International before it was closed in 1991 in a massive fraud case, and later acknowledged that he had solicited a $10 million loan from the bank for a business associate.

During the opioid crisis in 2015, he introduced a bill to narrow the authority of government regulators to halt the marketing of drugs by predatory pharmaceutical companies. It later emerged that he had received $2.3 million in donations from the drug industry over 25 years.

But there were no political repercussions. The senator was re-elected in 1982, 1988, 1994, 2000, 2006 and 2012, averaging nearly 65 percent of the vote.

Orrin Grant Hatch was born in Homestead Park, Pa., near Pittsburgh, on March 22, 1934, the sixth of nine children of Jesse and Helen (Kamm) Hatch. His parents were Mormons who had moved from Utah in the 1920s to find work. After losing their home in the Depression, Jesse borrowed $100 to buy a plot of land in the hills above Pittsburgh and built a house of blackened lumber salvaged from a fire.

Two of Orrin’s siblings died in infancy. He was deeply affected by the loss of his brother, Jesse, a World War II Army Air Force nose gunner who was killed when his B-24 was shot down in a 1945 bombing raid over Europe.

At Baldwin High School, Orrin was captain of the basketball team and president of the student body. He took two years off for missionary work, proselytizing in Ohio, and graduated in 1955. He then moved to Utah and worked as a union lathe operator to pay his way through Brigham Young University.

In 1957, he married Elaine Hansen. They had six children: Brent, Marcia, Scott, Kimberly, Alysa and Jess.

After earning a bachelor’s degree in history at BYU in 1959, he studied law at the University of Pittsburgh on a full scholarship and received his juris doctor in 1962. He joined a Pittsburgh law firm, but in 1969 moved to Salt Lake City to open his own practice. He represented private clients in tax, contract and personal injury cases, and corporations fighting federal regulations.

Coming from a family of Roosevelt Democrats, Mr. Hatch gradually became a conservative Republican. Upset by many events, including the Supreme Court’s ban on public-school prayers and its legalization of abortion in Roe v. Wade, he concluded that America was headed in the wrong direction.

“I was convinced that someone needed to stand against these trends,” he said in his memoir. “Someone needed to point out the deterioration of our moral fiber, the proliferation and increasing acceptance of drugs and crime, the expansion of the welfare state.”

That someone was he.