Joseph I. Lieberman, Connecticut’s four-term United States senator and Vice President Al Gore’s Democratic running mate in the 2000 presidential election, which was won by George W. Bush and Dick Cheney when the Supreme Court halted a Florida ballot recount, died on Wednesday in Manhattan. He was 82.

His family said in a statement that the cause was complications of a fall. His brother-in-law Ary Freilich said that Mr. Lieberman’s fall occurred at his home in the Riverdale section of the Bronx and that he died at NewYork-Presbyterian Hospital in Upper Manhattan.

At his political peak, on the threshold of the vice presidency, Mr. Lieberman — a national voice of morality as the first major Democrat to rebuke President Bill Clinton for his sexual relationship with the White House intern Monica Lewinsky — was named Mr. Gore’s running mate at the Democratic National Convention that August in Los Angeles. He became the nation’s first Jewish candidate on a major-party presidential ticket.

In the ensuing campaign, the Gore-Lieberman team stressed themes of integrity to sidestep the Clinton administration’ scandals, and Mr. Lieberman urged Americans to bring religion and faith more prominently into public life.

The ticket won a narrow plurality of the popular votes — a half-million more than the Bush-Cheney Republican ticket. But on the evening of Election Day, no clear winner had emerged in the Electoral College, and an intense legal struggle took center stage.

After weeks of dispute, it came down to the results in Florida, where fewer than 600 votes appeared to separate the opposing candidates. In an unsigned landmark decision on Dec. 12, the United States Supreme Court ruled, 5-4, that different standards of recounting in different counties had violated the equal protection clause of the Constitution and ordered an end to the recounts. The decision effectively awarded Florida’s 25 electoral votes, and the presidency, to Mr. Bush.

“It was a miscarriage of justice on two levels,” Mr. Lieberman said in a 2023 interview for this obituary. “One was that the Florida Supreme Court had already ruled in our favor to continue the recounts, and the other was that it was an extrajudicial political decision made in the crisis of a transition of power, and out of line with precedents of the Supreme Court.”

Mr. Lieberman sought the 2004 Democratic presidential nomination but lost multiple primaries and withdrew from the race in February. He believed his support for the war in Iraq had doomed his candidacy.

Even his standing with Connecticut voters had slipped. Running for a fourth Senate term in 2006, he lost the Democratic primary to an antiwar candidate but won in a stunning upset in the general election as a third-party independent on the “Connecticut for Lieberman” ballot line.

With his presidential hopes in tatters, Mr. Lieberman in 2008 attended the Republican National Convention and endorsed his friend, Senator John McCain of Arizona, for the presidency. Mr. McCain had Senator Lieberman vetted as a possible running mate but ultimately chose Gov. Sarah Palin of Alaska and lost the election to Senator Barack Obama.

Mr. Lieberman, a virtual outcast in his own party, had stopped attending Democratic Senate caucuses. But after a humbling meeting with the Senate majority leader, Harry Reid, he was allowed to keep his Homeland Security Committee chairmanship and resumed caucusing with the party.

Approaching Senate retirement, he endorsed no one in the 2012 presidential election, but he supported Secretary of State Hillary Clinton in her presidential run against Donald J. Trump in 2016 and Vice President Joseph R. Biden’s victory over Mr. Trump in 2020.

During his Senate tenure from 1989 to 2013, Mr. Lieberman was an independent who wore no labels easily. He called himself a reform, centrist and moderate Democrat, but he generally sided with the Democrats on domestic issues, like abortion choices and civil rights, and with the Republicans on foreign and defense policies.

He supported Israel and called himself an “observant” Jew but not an Orthodox one because he did not follow strict Orthodox practices. His family kept a kosher home and attended Sabbath services. To avoid conveyances on a Sabbath, he once walked across town to the Capitol to block a Republican filibuster after attending services in Georgetown.

Many Democrats criticized Mr. Lieberman’s support for the war in Iraq, but admirers said his strengths with voters lay in his rectitude, his religious faith and his willingness to compromise.

“He may be a thoroughgoing moderate in his politics, but he is a true conservative in temperament and style,” The New Yorker said in a 2002 profile. “His world is an orderly place where people wait in line, take their turns and generally behave themselves.”

After the terrorist attacks of Sept. 11, 2001, Mr. Lieberman led the Senate effort to create a new Department of Homeland Security, a cabinet agency that consolidated 22 federal entities to counter terrorism and coordinate responses to natural disasters. He was named chairman of the new Senate Committee on Homeland Security in 2003.

He also cast the 60th and deciding vote under Senate rules to pass Mr. Obama’s Affordable Care Act in 2010 — the most important package of health care legislation since the creation of Medicare and Medicaid in 1965.

“As a Democrat, Joe wasn’t afraid to engage with Senators from across the aisle and worked hard to earn votes from outside his party,” Mr. Bush said in a statement after Mr. Lieberman’s death. “He engaged in serious and thoughtful debate with opposing voices on important issues.”

A Yale-educated lawyer, Mr. Lieberman began his political career in 1970 by unseating Ed Marcus, the Connecticut State Senate’s Democratic majority leader. He credited a young Yale law student on his staff, Bill Clinton, with engineering his crucial primary victory.

After a decade in the State Senate, the last six years of which he was the Democratic majority leader, Mr. Lieberman lost a race for a seat in the House of Representatives in 1980. Three years later, he was elected attorney general of Connecticut, the first to hold the post full-time. In that office, he defended consumer and environmental protections and was re-elected in 1986, but he left the job after winning his first Senate race in 1989.

In the Senate, he supported free trade and unions and led a campaign against sex and violence in video games. The effort generated a video ratings system in the 1990s and national publicity for Mr. Lieberman.

His campaign for a second term in 1994 scored the largest landslide ever in a Connecticut Senate race: He collected 67 percent of the ballots and buried his foe by 350,000 votes. For six years, he was chairman of the Democratic Leadership Council. And in 1998, when Bill Clinton’s affair with Ms. Lewinsky broke, Mr. Lieberman chastised the president publicly.

“It was a very hard thing for me to do because I liked him,” he told Bill Kristol, the neoconservative commentator. “But I really felt what he did was awful.” A remorseful Mr. Clinton later called Mr. Lieberman, saying, “I just want you to know that there’s nothing you said in that speech that I disagree with.”

In 2000, while running for the vice presidency on Mr. Gore’s ticket, Mr. Lieberman simultaneously won a third term in the Senate handily, with 64 percent of the vote, turning back a challenge from the Republican Philip Giordano. But six years later, Mr. Lieberman hit a wall seeking a fourth term. Ned Lamont, a Greenwich businessman and critic of the Iraq war, won 52 percent of the vote in a primary.

Ordinarily, losing a primary is a death knell: Campaign donations dry up, colleagues and the press turn away, and the loser drops out or runs as an independent.

However, Mr. Lieberman refused to give up. Many voters saw the race as a referendum on President Bush, whose claims that President Saddam Hussein of Iraq had weapons of mass destruction had been disproved, suggesting that he had taken the nation to war under false pretenses. With wide Republican endorsements, Mr. Lieberman easily defeated Mr. Lamont in the general election for one last Senate term. (Mr. Lamont became Connecticut’s governor in 2019.)

Mr. Lieberman was also instrumental in Mr. Obama’s successful 2010 effort to repeal a 17-year-old “Don’t ask, don’t tell” Armed Forces policy, which had forced gay and lesbian service members to be closeted or face discharges.

On Jan. 2, 2013, Mr. Lieberman gave a parting address in the Senate. “It was a lonely farewell,” The Washington Post said. “As Mr. Lieberman plodded through his speech, thanking everybody from his wife to the Capitol maintenance crews, a few longtime friends trickled in.” They included Senators Susan Collins, John Kerry and John McCain.

“The sparse attendance wasn’t unusual for a farewell speech,” The Post said, “but it was a sad send-off for a man who was very close in 2000 to becoming a major figure in American political history as the first Jew on a major party’s national ticket. He was denied the vice presidency not by the voters but by the Supreme Court.”

Joseph Isadore Lieberman was born in Stamford, Conn., on Feb. 24, 1942, the oldest of three children of Henry and Marcia (Manger) Lieberman. His father owned a liquor store while his mother managed the home.

Joe and his sisters, Rietta and Ellen, grew up in a working-class section of Stamford. He attended Burdick Junior High School and Stamford High School, where he was elected president of his sophomore and senior classes, joined a debating club and was salutatorian of the class of 1960.

At Yale, he majored in political science and economics, joined the N.A.A.C.P. and the Democratic Party and was the editor, chairman and chief editorial writer of The Yale Daily News, writing about defending the civil rights of Black Southerners. He graduated magna cum laude with a bachelor’s degree in 1964 and received his law degree from Yale in 1967.

His marriage in 1965 to Betty Haas ended in divorce in 1982. That same year, he married Hadassah Freilich Tucker, a daughter of Holocaust survivors. He is survived by his wife; two children from his first marriage, Matthew and Rebecca Lieberman; a daughter from his second marriage, Hana Lieberman; a stepson from his second marriage, Ethan Tucker; two sisters, Rietta Miller and Ellen Lieberman; and 13 grandchildren.

After leaving the Senate in 2013, Mr. Lieberman moved to Riverdale and joined the Manhattan law firm Kasowitz, Benson, Torres & Friedman, which specialized in white-collar defense. Its clients included Mr. Trump during his years as a bankruptcy-troubled casino magnate.

In recent years Mr. Lieberman helped lead the bipartisan political organization No Labels as its founding chairman and recently as its co-chairman.

In 2017, Mr. Trump interviewed Mr. Lieberman for the position of F.B.I. director, to replace the fired James Comey, but Mr. Lieberman withdrew from consideration. He criticized Mr. Trump’s retreat from the Paris climate-change accords and his handling of the coronavirus pandemic. After Mr. Trump lost his 2020 re-election bid, Mr. Lieberman rejected the former president’s false claims that he had won.

In an interview with CNN weeks later, Mr. Lieberman denounced Mr. Trump as a threat to democracy. “Trump lost by seven million votes, and he’s hurting our democracy, and frankly hurting himself with this crazy business,” Mr. Lieberman said. “It’s a terrible thing he’s doing. There is no evidence of fraud.”

Anastasia Marks contributed reporting.