Harry M. Reid, the Democrat who rose from childhood poverty in the rural Nevada desert to the heights of power in Washington, where he steered the Affordable Care Act to passage as Senate majority leader, died on Tuesday in Henderson, Nev. He was 82.

Mr. Reid had been treated for pancreatic cancer, which was diagnosed in 2018, but lived to see the Las Vegas airport renamed for him earlier this month. His death was confirmed in statements from Gov. Steve Sisolak of Nevada and Senator Chuck Schumer, Democrat of New York and the majority leader.

Even by the standards of the political profession, where against-the-odds biographies are common and modest roots an asset, what Mr. Reid overcame was extraordinary. He was raised in almost Dickensian circumstances in tiny Searchlight, Nev.: His home had no indoor plumbing, his father was an alcoholic miner who eventually committed suicide, and his mother helped the family survive by taking in laundry from local brothels.

After two decades of campaigns in Nevada marked by success, setback and recovery, Mr. Reid was elected to the Senate in 1986. He became the chamber’s Democratic leader after the 2004 election.

But it was not until his colleague Barack Obama was elected president four years later that Mr. Reid was able to meld his deep knowledge of congressional rules, his facility with horse-trading and his cussed determination to unify his 60-seat majority and pass landmark legislation.

Pushing through a sweeping economic stimulus after the Great Recession, a new set of rules governing Wall Street and the most significant expansion of health care coverage since the Great Society of the 1960s, all with scant Republican support, Mr. Reid became, along with House Speaker Nancy Pelosi, one of the indispensable lawmakers of the Obama era.

“The records will be written about the eight years of Obama and Reid,” Mr. Reid boasted shortly after he announced in 2015 that he would not seek re-election the following year.

Yet the three-decade Senate tenure of this soft-spoken yet ferociously combative Nevadan, a middleweight boxer in his youth, also traced the chamber’s evolution from a collegial and consensus-oriented institution to the partisan and fractured body it has become. Republicans placed some of the blame on Mr. Reid for this change, pointing to his 2013 decision to upend Senate rules by doing away with the filibuster on most nominations by a president.

Mr. Reid, though, reflected the broader leftward shift of his party and his state. First elected to the House of Representatives in 1982, when Nevada finally grew large enough to require a second seat, he arrived in the capital as a moderate western Democrat: opposed to abortion rights, largely supportive of gun rights and uneasy about immigration.

But as Nevada grew from an overwhelmingly rural, white redoubt of ranches and mines to a polyglot gambling mecca in which 70 percent of voters live in the Las Vegas area, Mr. Reid adapted as a matter of necessity. He won his final re-election in 2010, a dismal year for Democrats nationally, thanks in part to an outpouring of support from his state’s rapidly growing Hispanic and Asian communities after his popularity among many other Nevadans had plummeted in the economic collapse.

“I may have won without them, but I doubt it,” Mr. Reid said in a later interview about his support among immigrants in his 2010 campaign.

But after Democrats lost the Senate majority in 2014, and after he had lost nearly all his sight in his right eye the next year in a serious accident in his home during a workout, Mr. Reid decided not to run for a sixth term. He said he did not want to be one of those senators who served well into old age.

While he was willing to adjust with the times politically, he remained a stylistic throwback. A Mormon who neither drank nor smoked, he also shunned his state’s principal industry, claiming with his characteristic bluntness that “the only people who make money from gambling are the joints and government.”

Prone to ‘Reidisms’

Mr. Reid was a meandering and awkward public speaker, far more comfortable plotting strategy beneath the imposing portrait of Mark Twain in his Capitol office than he was making the case for his party on a Sunday news show, much less at a political rally.

In private, he wielded an irreverent sense of humor, but could be brusque, often not even saying goodbye to colleagues at the end of a phone call. When he did speak publicly or to the press, he was often given to verbal miscues that came to be known as “Reidisms.”

He deemed President George W. Bush “a loser” while addressing a group of high school juniors in Nevada in 2005, mused about the body odor of Washington’s tourists a few years later and, when Mr. Obama first ran for president, in 2008, said the country’s first Black president could be elected because he spoke “with no Negro dialect, unless he wanted to have one.” (Mr. Reid telephoned Mr. Obama to apologize after the comments were made public; Mr. Obama issued a statement calling the remarks “unfortunate,” but added, “I know what’s in his heart.”)

It was Mr. Reid who saw Mr. Obama’s potential for a successful run at the White House when many Democrats were rallying behind Hillary Clinton. Recognizing that the young Illinois senator had little affection for the Senate’s byzantine ways, Mr. Reid in 2006 privately urged him to mount a bid for the Democratic nomination. “I am one of the reasons he’s president,” Mr. Reid told The Washington Post after announcing his retirement.

Mr. Obama confirmed as much Tuesday evening, when he posted on Twitter a letter he had recently written to Mr. Reid.

“I wouldn’t have been president had it not been for your encouragement and support, and I wouldn’t have got most of what I got done without your skill and determination,” Mr. Obama wrote.

Mr. Reid was as shrewd a tactician as he was poor a communicator, and nowhere was that more evident than in Nevada, where he became the state’s dominant political figure for the final two decades of his life — “a Machiavelli with malaprops,” as the Las Vegas-based journalist Jon Ralston called him.

Mr. Reid used his position on the Senate Appropriations Committee and his eventual majority leadership to block nuclear waste from being deposited in Nevada’s Yucca Mountain, a decades-long fight, while relentlessly earmarking spending for his state, where 85 percent of the land was federally owned when he left office. He also helped create Nevada’s Great Basin National Park, ensured that millions of acres in the state were protected as national parks or monuments, and made sure that federal funds were directed to cleaning and preserving Lake Tahoe, which straddles Nevada’s border with California.

Mr. Reid ran Nevada’s Democratic Party in the manner of an old-style political boss, determining which candidates would run up and down the ballot, arranging his own succession and even remaining in charge after his cancer diagnosis and through the 2018 midterm elections, nearly two years after his retirement from the Senate.

He also used his clout to elevate his state’s role in the presidential nominating process, moving Nevada’s caucuses up to become one of the early voting states in the Democratic primaries, and in 2016 he quietly helped Mrs. Clinton salvage her nomination there.

A Difficult Start

Harry Mason Reid Jr. was born on Dec. 2, 1939, in Searchlight, a mining outpost that had about 200 residents in his youth. One of four sons of Harry Sr. and Inez (Jaynes Reid), he grew up in privation. His father suffered from depression and was often unemployed. Harry worked at a gas station in high school, earning enough money to purchase his mother a new set of false teeth.

Boxing metaphors about Mr. Reid would eventually become clichéd — he even named his memoir “The Good Fight” — but he was quite the pugilist. He got into physical altercations with his father (when his father would become violent toward his mother) and with his future father-in-law (who was uneasy about his daughter marrying Mr. Reid).

To attend high school, he would hitchhike 40 miles to Henderson, near Las Vegas, where he had relatives. And it was there that his political career effectively began. He had a teacher and boxing coach named Mike O’Callaghan, who would be elected governor in 1970 with Mr. Reid as his running mate.

With financial assistance from Nevada businessmen, Mr. Reid graduated from Utah State University, where he converted to Mormonism. He then attended law school at George Washington University in Washington, D.C., moonlighting as a Capitol Police officer to pay his way through.

With his law degree, he returned to Nevada and became the local prosecutor in Henderson. He was elected to the Nevada State Assembly in 1968. Two years later, he and Mr. O’Callaghan were elected statewide.

Then, unexpectedly, Senator Alan Bible, a Democrat, announced in 1974 that he would not run for re-election. Mr. Reid won his party’s nomination but lost in the general election to Paul Laxalt, a popular former Republican governor, by fewer than 700 votes. It was the only Democratic Senate seat in the country that year that Republicans picked up.

In an early demonstration of his political pugnacity, Mr. Reid had demanded during the campaign that Mr. Laxalt release his family’s financial interests.

“One problem,” Mr. Reid recalled with a chuckle years later. “His sister was a nun. I got killed on that.”

After an ill-fated bid for the Las Vegas mayoralty in 1975, Mr. Reid’s career was floundering. But Mr. O’Callaghan again came to his aid, making Mr. Reid chairman of the Nevada Gaming Commission at a moment when state officials were trying to root out the mob from Las Vegas’s casinos.

It was only then that Mr. Reid realized how entrenched the mob still was on the city’s famous Strip. “That was a real eye-opener for me,” he said later, “because I thought I knew the state very well, but I didn’t.”

As gaming commissioner, he was offered bribes and participated in F.B.I. stings. Near the end of his tenure, his wife, Landra Reid, came out of their house one day to find a bomb attached to the family’s station wagon.

Ms. Reid, who was his closest adviser, survives him, as do his children, Rory, Lana Reid Barringer, Leif, Josh and Key, and 19 grandchildren.

Following the 1980 census, Nevada, for the first time in its history, had a large enough population to merit a second House seat, representing the Las Vegas area. Mr. Reid won the new district, but after two terms a Senate seat again opened up, thanks to Mr. Laxalt’s retirement.

Mr. Reid again benefited from running in a good Democratic year, in 1986, and this time his bare-knuckled tactics paid off as he handily defeated Mr. Laxalt’s hand-picked successor, former Representative Jim Santini.

He won a coveted seat on the Appropriations Committee in his first term and spent much of the first part of his career looking out for the needs of Nevada, which was beginning to boom as a global hospitality capital.

After another agonizingly close race in 1998 — he won by fewer than 500 votes following a recount — Mr. Reid was elected minority whip, the second-ranking Senate Democrat. Though still not a prominent figure in Washington, he was pivotal in wooing Senator Jim Jeffords of Vermont to leave the Republican Party in 2001 and caucus with the Democrats, a move that gave Mr. Reid’s party control of the narrowly divided Senate.

After Senator Tom Daschle, the Democratic leader, was defeated in 2004, Mr. Reid effectively secured the commitments he needed to take over the caucus by the next day.

The Majority Leader

A fierce critic of President Bush — he called him “a liar” as well as a loser — Mr. Reid became a beneficiary of the president’s unpopularity in 2006, when Democrats took back control of the Senate and Mr. Reid became majority leader. He played a key role in passing the bank bailout after the stock market collapsed in the fall of 2008. Later that year, when Mr. Obama was elected, Democrats made even more gains, giving Mr. Reid a filibuster-proof majority.

But the Democratic caucus included senators across the ideological spectrum and, with few moderate Republicans left, it took all of Mr. Reid’s legislative acumen, doggedness and even shamelessness to win some close votes. On the health law, for example, he offered Senator Ben Nelson of Nebraska a generous expansion of Medicaid funding in his state, a deal that critics called “the Cornhusker Kickback.”

Mr. Reid’s hard-nosed tactics handed Democrats a series of major achievements, but he enraged Republicans and was vulnerable to defeat entering what would be his final re-election campaign in 2010.

He overcame his own unpopularity by meddling in the Republican primary, as his allies undermined a potentially strong candidate and helped lift a far-right conservative, Sharron Angle, who was herself as gaffe-prone as Mr. Reid. He won the general election comfortably even as the rise of the Tea Party movement propelled Republicans to victory across the country.

That same single-mindedness and indifference to criticism, however, even embarrassed some of his allies two years later when he sought to undermine Mitt Romney’s presidential candidacy in 2012 by repeatedly, and without evidence, claiming that Mr. Romney had gone a decade without paying income tax.

Mr. Reid was even more contemptuous of former President Donald J. Trump, calling him “a racist” and “sexual predator” who achieved prominence only because of the fortune he had inherited.

Being born into wealth was, of course, alien to Mr. Reid. At the end of his career — after great financial and political success and raising five children, one of whom became an elected official in Las Vegas — he relished showing visitors his dusty hometown. But he recalled that it was not until he saw Alex Haley give a talk about his book “Roots” that he stopped feeling ashamed by his impoverished background.

“He said be proud of who you are, you can’t escape who you are,” Mr. Reid said in his Senate farewell speech, adding that at that point he proudly became “Harry Reid, the guy from Searchlight.”