He made the announcement without securing a plea bargain with federal prosecutors, though a law enforcement official said the former governor was still believed to be negotiating one. The official spoke on condition of anonymity because of the sensitivity of the case.
Spitzer will be succeeded on Monday by Lt. Gov. David Paterson, a fellow Democrat who becomes New York's first black governor and the nation's first legally blind chief executive.
The resignation brought the curtain down on a riveting three-day drama - played out, sometimes, as farce - that made Spitzer an instant punchline on late-night TV and fascinated Americans with the spectacle of a crusading politician exposed as a hypocrite.
His dizzying downfall was met with glee and the popping of champagne corks among many on Wall Street, where Spitzer was seen as a sanctimonious bully for attacking big salaries and abusive practices in the financial industry when he was New York attorney general. And his resignation brought relief at the state Capitol in Albany after days of excruciating tension and uncertainty.
"Some rules can't be broken, and when they are broken there are consequences," said state Assemblyman John McEneny, a Democrat. "In this case, one of the most promising careers I've seen in a generation."
The scandal erupted Monday after federal law enforcement officials disclosed that a wiretap had caught the 48-year-old father of three teenage daughters spending thousands of dollars on a call girl at a fancy Washington hotel on the night before Valentine's Day.
Investigators said he had arranged for a prostitute named Kristen to take the train down from New York while he was in the nation's capital to testify before a congressional subcommittee about the bond industry.
Late Wednesday, the New York Times reported that her real name is Ashley Alexandra Dupre. She declined to comment when asked by the Times when she first met Spitzer and how many times they had been together.
It was unclear whether she would face charges; attorney Don D. Buchwald confirmed that he represents the same woman in the Times story but wouldn't comment further.
With every development, it became increasingly clear that Spitzer, politically, was finished.
Law enforcement officials said the governor - the millionaire heir to a New York real estate fortune - had hired prostitutes several times before and had spent tens of thousands of dollars, and perhaps as much as $80,000, on the high-priced escort service Emperors Club VIP, whose women charge as much as $5,500 an hour.
Senior Spitzer aides, speaking on condition of anonymity because of the sensitivity of the matter, said Spitzer had been informed Friday by federal prosecutors that he was linked to the prostitution ring.
They said he had kept it to himself through Saturday night, when he attended the annual dinner of the Gridiron Club in Washington.
That night a reporter kept calling cell phones of Spitzer aides.
Spitzer first shared the news Sunday with his wife at their Manhattan apartment, and after several excruciating hours they told their daughters, the aides said. By Sunday evening Spitzer had called top advisers, personal friends and loyalists. The little band huddled in the apartment until midnight.
After making a watery-eyed, non-specific public apology Monday with his wife by his side, Spitzer continued to talk to family and advisers through Tuesday. By Wednesday morning, aides said, he had decided to resign.
He and his wife rode in a black SUV from their Fifth Avenue apartment to his New York City office to announce his resignation - a trip whose every move was captured by TV helicopters. During the news conference, he and his wife stood inches apart, never touching as they entered or left the room.
Speaking in a strong and steady voice, he apologized for his actions and said: "Over the course of my public life, I've insisted, I believe correctly, that people regardless of their position or power take responsibility for their conduct. I can and will ask no less of myself."
He did not address the allegations in any detail in the less than three-minute statement, and left without taking questions.
Officials said that Paterson asked for the Monday hand-over because he needed more time to prepare and wanted Spitzer to say the proper goodbye to his staff.
In a statement issued after Spitzer quit, U.S. Attorney Michael Garcia, the chief federal prosecutor in New York, said: "There is no agreement between this office and Gov. Eliot Spitzer relating to his resignation or any other matter."
Among the possible charges that law enforcement authorities said could be brought against the former governor: soliciting and paying for sex; violating the Mann Act, the 1910 federal law that makes it a crime to take someone across state lines for immoral purposes; and illegally arranging cash transactions to conceal their purpose.
Spitzer, a graduate of Princeton University and Harvard Law, could also be disbarred. In New York, an attorney can lose his license to practice law for failing to "conduct himself both professionally and personally, in conformity with the standards of conduct imposed upon members of the bar."
It was a spectacular collapse for a man who cultivated an image as a hard-nosed politician hell-bent on cleansing the state of corruption. He served two terms as New York attorney general, earning the nickname "Sheriff of Wall Street," and was elected governor with a record share of the vote in 2006. The tall, athletic, square-jawed Spitzer was sometimes mentioned as a potential candidate for president.
But he also made powerful enemies, many of whom complained that he was abusive and self-righteous.
"I really don't feel vindicated," said John Faso, the Republican who lost to Spitzer for governor. But he added: "One of the many things I said was that Eliot Spitzer had one set of rules for himself and one set for everyone else. I never would have imagined it could be so glaring."
Traders on the floor of the New York Stock Exchange were transfixed by TV monitors broadcasting Spitzer's resignation, and his ruin drew scattered applause from traders as they went about buying and selling stocks. One trader said some firms even cracked champagne open - a ritual usually reserved for when the Dow hits a milestone.
Paterson said in a statement that he was saddened, but added: "It is now time for Albany to get back to work as the people of this state expect from us."
Barely known outside of his Harlem political base, Paterson, 53, has been in New York government since his election to the state Senate in 1985.
Though legally blind, he has enough sight in his right eye to walk unaided, recognize people at conversational distance and even read if the text is placed close to his face.
While Spitzer was famously abrasive, uncompromising and even insulting, Paterson has built a reputation as a conciliator, and lawmakers quickly embraced the new order.
"The first thing he can and I think he will do is end the era of accusation and contempt and ridicule," said Democratic Assemblyman Richard Brodsky. "I think everyone will be better off because of it."
