ALBANY, N.Y. — Sheldon Silver, the once-indomitable leader of the New York State Assembly whose career and reputation were undone by a 2015 corruption conviction, died on Monday. He was 77.

Mr. Silver had been incarcerated at Devens Federal Medical Center in Ayer, Mass., according to Judith Rapfogel, his former chief of staff. Kristie Breshears, a spokeswoman for the federal Bureau of Prisons, said in a statement that Mr. Silver had died at the nearby Nashoba Valley Medical Center.

The cause of death was not immediately clear, but Mr. Silver had a history of cancer and chronic kidney disease, according to statements made by his lawyers in 2020.

A Lower East Side Democrat whose rise to power began with his election in 1976, Mr. Silver was known as a master of Albany’s often labyrinthian levers of power, controlling the Assembly — and its dominant Democrat majority — as its speaker for two decades, from 1994 to 2015.

Soft-spoken and sphinxian in his public statements and Capitol-corridor interviews, Mr. Silver nonetheless wielded outsize influence, capable of pushing liberal causes like raising the minimum wage and building affordable housing. At the same time, he was also capable of thwarting priorities of mayors and governors — he served alongside six, from Hugh L. Carey to Andrew M. Cuomo — when he cared to, including such flashy proposals as a stadium on the West Side of Manhattan.

That dominance came tumbling down in early 2015 when Mr. Silver was accused of accepting nearly $4 million in illicit payments in exchange for taking official actions for a cancer researcher at Columbia University and two real estate developers.

Found guilty of federal corruption charges in late 2015, Mr. Silver managed to successfully challenge that conviction, resulting in its being overturned in 2017. A second trial — and a second conviction — followed in 2018. Mr. Silver managed to avoid prison until 2020, when his legal machinations finally ground to a halt, leaving him to serve a six-and-a-half-year sentence.

Mr. Silver won a brief reprieve from prison life last spring when he was furloughed because of the coronavirus pandemic. After a public outcry, Mr. Silver was returned to prison two days later.

On Monday, longtime former colleagues of Mr. Silver sought to reconcile the circumstances of his downfall with what they see as his achievements during 20 years as the leader of the Assembly.

“Shelly Silver was one of the strongest forces for progressive issues in the New York State Legislature,” said Assemblyman Richard Gottfried, a Democrat from Manhattan, highlighting Mr. Silver’s record on civil liberties issues, reproductive rights and recognizing same-sex marriage. “I was always struck by how strong his personal beliefs in progressive causes were.

“It’s a tragedy that those achievements have been overshadowed by his criminal record,” said Mr. Gottfried, the longest-serving state lawmaker in New York’s history. “I don’t think anyone in Albany had any inkling of the things that came out in his criminal case.”

Assemblyman Charles D. Lavine, a Democrat from Long Island, said Mr. Silver would be remembered for being a fierce defender of New York City’s priorities, including in the aftermath of 9/11, and for forcefully pursuing liberal policies around housing and education. Mr. Lavine said Mr. Silver to “did some wonderful things for our state,” but added that the politician “brought shame on our state and on his name.”

His downfall — and that of his Republican counterpart in the State Senate, Dean G. Skelos, who was also convicted of federal corruption charges in 2015 — presaged a shifting balance of power in Albany, where most deals were traditionally brokered by “three men in a room,” meaning the governor, speaker of the Assembly and Senate leader.

Indeed, Mr. Silver’s successor, Carl E. Heastie, a Bronx Democrat who is also the Assembly’s first Black speaker, has been considered more of a consensus seeker than the iron-fisted Mr. Silver. And the historical convention of “three men” making important decisions has also been shelved, at least temporarily, as the jobs of governor and leader of the State Senate are now filled by women.

The son of Russian immigrants, Sheldon Silver was born on Feb. 13, 1944, on the Lower East Side, a working-class neighborhood that he would call his lifelong home and that helped to form both his political beliefs and his base of power. He trained as a lawyer — earning a degree from Brooklyn Law School — but also enjoyed more street-level activities, playing basketball on the city’s public courts, a passion he shared with former Gov. Mario M. Cuomo and other city lawmakers.

He ran for Assembly in 1976, crushing a Republican opponent, Leonard Wertheim, and joining a chamber that included Chuck Schumer — now the state’s senior U.S. senator. Mr. Silver rose in the ranks, eventually becoming the chairman of the Codes Committee, which oversees criminal law, and continued to practice law, two threads that would collide in his eventual corruption conviction.

Early political victories reflected his legislative savvy and his religious faith: An Orthodox Jew, he sponsored a 1983 law that abolished religious barriers to remarriage for Jewish women — who required a “get,” or Jewish divorce decree, from their husbands — in opposition to traditional Jewish law. He also helped outlaw autopsies when the procedure was contrary to religious belief and had no “compelling public necessity,” according to his Assembly biography.

His rise to speaker came via tragedy in 1994, when then-Speaker Saul Weprin died from complications of a stroke. Mr. Silver had been serving as interim speaker, ascending to the job with the support of other New York City Democrats, who wield profound power in the Assembly.

Making deals with the State Senate, ruled by Republicans, required a deft negotiator, according to Joseph R. Lentol, a former Democratic assemblyman from Brooklyn, who said Mr. Silver played a key role in securing state money in the early 1990s to fund the hiring of police officers in the city, clean up Times Square and help spark “the renaissance of New York City.”

“He was able to work things out and make compromises with a Republican Senate and very often a Republican governor,” Mr. Lentol said, noting that Mr. Silver had served for 12 years under Gov. George E. Pataki, a three-term Republican.

In 2000, Mr. Silver faced a revolt on the Assembly floor from a faction of Democrats, many of them from upstate, who were dissatisfied with his leadership. The attempt at a coup failed, but it wounded Mr. Silver politically and made public a remarkable intraparty power struggle that would have typically played out behind closed doors in the Capitol.

In 2007, Mr. Pataki was replaced by Gov. Eliot Spitzer, beginning a streak of Democratic governors in New York that continues to today. But even as governors — and New York City mayors — came and went, Mr. Silver continued to serve, becoming perhaps the most powerful man in the state, able to shape legislative agendas and multibillion-dollar budgets to his will.

At the same time, his legal practice continued to churn, eventually leading to his indictment and arrest on charges that he had steered grants to a Columbia University cancer researcher, Robert N. Taub, in exchange for referring cancer patients to a law firm, Weitz & Luxenberg, which kicked back part of its fees to Mr. Silver. Another scheme involved similar fees being paid to Mr. Silver by two real estate developers.

His arrest in 2015 rocked Albany, upending years of stability and opening the door for a wave of young, more progressive lawmakers, a trend that eventually led to Democrats’ capturing the State Senate in 2018.

During his sentencing last year amid the pandemic, Mr. Silver’s lawyers asked a judge to allow him to avoid prison and serve a term of home confinement, arguing that imprisonment would increase his chances of becoming ill or contracting the coronavirus. Judge Valerie E. Caproni of Federal District Court in Manhattan, who oversaw the case, denied the request.

“Your honor, I do not want to die in prison,” Mr. Silver had written the judge.

Mr. Silver is survived by his wife, Rosa, and four children, Edward, Esther, Janine and Michelle.

William K. Rashbaum contributed reporting.