Sheldon Silver, who rose from the Lower East Side of Manhattan to become one of the state’s most powerful and feared politicians as speaker of the New York Assembly, was sentenced on Tuesday to 12 years in prison in a case that came to symbolize Albany’s culture of graft.

The conviction of Mr. Silver, 72, served as a capstone to a campaign against public corruption by Preet Bharara, the United States attorney for the Southern District of New York,which has led to more than a dozen state lawmakers’ being convicted or pleading guilty.

But none had the power, cachet or longevity that Mr. Silver, a Democrat, had enjoyed, and prosecutors sought to make an example of him. They asked that he receive a sentence greater than the terms that had been “imposed on other New York State legislators convicted of public corruption offenses.”

The longest such sentence cited by the government was 14 years, the term imposed last year in the case of another former Democratic assemblyman, William F. Boyland Jr., who was tried and convicted in federal court in Brooklyn.

Carrie H. Cohen, an assistant United States attorney, asked that Mr. Silver’s sentence “reflect the massive damage caused to the public by his crimes.”

The sentence, Ms. Cohen continued, should “send a message that this is not how business is done in Albany,” adding that “no one, including Sheldon Silver, is above the law.”

Mr. Silver briefly addressed the court before his sentence was delivered, saying he had let down his constituents, family and colleagues. “I’m truly, truly sorry for that,” he said.

The judge, Valerie E. Caproni, said at first that the many letters written on Mr. Silver’s behalf demonstrated that he went “above and beyond the call of duty many times.” But she then outlined why she thought Mr. Silver deserved a serious sentence, certainly one that went far beyond the community service his lawyers had requested.

Judge Caproni said that there had been an “incalculable harm to the people of New York,” and that the cumulative effect of public corruption “makes the public very cynical.” She then listed some of Mr. Silver’s misdeeds, and addressed him directly: “Mr. Silver, those are not the actions of an honest person.”

Mr. Silver was convicted on Nov. 30 of charges that included honest services fraud, money laundering and extortion. Upon his conviction, he forfeited his Assembly seat. Two weeks later, Dean G. Skelos, who as majority leader had been Mr. Silver’s Republican counterpart in the State Senate, was also convicted of corruption.

Mr. Skelos is to be sentenced on May 12; a week later, John L. Sampson, a former leader of the Senate Democrats, will face his own sentencing. The scrutiny continues: Several inquiries are now focused on possible wrongdoing connected to the administrations of Gov. Andrew M. Cuomo and Mayor Bill de Blasio, both Democrats.

To date, however, Mr. Silver’s precipitous fall has no recent rival in the world of New York politics.

Mr. Silver had served for more than two decades as the Assembly speaker, imposing his will on matters large and small; he had a reputation as a staunch defender of New York City, a shrewd negotiator at budget talks and, at times, a recalcitrant opponent of anything he disliked.

But at a five-week trial in Federal District Court in Manhattan last fall, a different side of Mr. Silver emerged. Evidence showed that he had obtained nearly $4 million in illicit fees in return for taking official actions that benefited a prominent cancer researcher, Dr. Robert N. Taub, at Columbia University, and two real estate developers, Glenwood Management and the Witkoff Group.

Mr. Silver had expressed regret that his conviction — and the revelations of rampant kickbacks, bribes and influence-peddling — had made the State Capitol the object of ridicule. In a letter sent last month to Judge Caproni, he offered an emotional apology, saying that he had “failed the people of New York.”

His lawyers had argued that the former speaker should be allowed to use his “unique talents” to benefit others, and that a sentence of “extensive community service and little — if any — incarceration could do that.” On Tuesday, they suggested that he could work with the Fortune Society, which helps the formerly incarcerated.

“His obituary has already been written,” about his crimes, one of his lawyers, Joel Cohen, said. “Notwithstanding everything he has done.”

But prosecutors on Tuesday questioned the authenticity of Mr. Silver’s contrition, noting that he had insisted that he would be exonerated “until the very moment of the jury’s verdict.”

Judge Caproni, citing Mr. Silver’s age, said she would not adhere to sentencing guidelines that recommended a term of roughly 22 to 27 years, saying such a sentence would be “draconian and unjust.” The court’s probation office had recommended a 10-year sentence.

The judge, however, upheld the government’s request that Mr. Silver forfeit more than $5 million in proceeds from his crimes and pay a $1.75 million fine.

Mr. Silver must surrender himself by noon on July 1; his lawyers have requested that he serve at the Federal Correctional Institution in Otisville, N.Y., because of its familiarity with the housing of Orthodox Jewish prisoners.

In a statement issued moments after the sentencing, Mr. Bharara said that the “stiff sentence is a just and fitting end to Sheldon Silver’s long career of corruption.”

Last month, prosecutors, in a written submission to the judge, offered what they said was additional evidence of the ways Mr. Silver had abused his office “for personal benefit,” by helping two women with whom he had conducted extramarital affairs.

One of the women had regularly lobbied Mr. Silver on behalf of clients with business before the state; he had “used his official position,” prosecutors said, to help the other woman get a state job.