ABC News has learned that New York Lt. Gov. David Paterson confirmed the resignation to New York officials.
The resignation letter, which was drafted yesterday, is expected to be submitted to the New York secretary of state Wednesday morning, according to officials involved in the process. Paterson will be sworn in afterwards.
The Associated Press reports a top state official also said Spitzer will resign effective Monday.
Spitzer has been pressured to step down since Monday, when it was revealed that he had been caught on a wiretap spending $4,300 with the Emperors Club VIP call-girl service.
Some of the money went toward a night with a prostitute named Kristen, and the rest to be used as credit toward future trysts. The papers also suggested that Spitzer had done this before.
Spitzer formerly served as the state's attorney general, and was regarded as one of the most ethical politicians.
A poll released late Tuesday found that 70 percent of New Yorkers think Spitzer should resign, while 66 percent believe he should be impeached and removed from office if he doesn't.
"It's a big thumbs down," said Lee Miringoff, director of the Marist College Institute for Public Opinion, which conducted the poll. "It points to just how politically untenable his position is right now."
The case involving Spitzer started when banks noticed frequent cash transfers from several accounts and filed suspicious activity reports with the Internal Revenue Service, a law enforcement official told The Associated Press. The accounts were traced back to Spitzer, leading public corruption investigators to open an inquiry.
A law enforcement official said Tuesday that Spitzer had spent tens of thousands of dollars with the call-girl service Emperors Club VIP. Another official said the amount could be as high as $80,000. It was not clear over what period of time that was spent.
Still another law enforcement official said investigators found that during the Washington tryst, Spitzer used two rooms at the Mayflower Hotel - one for himself, the other for the prostitute. Sometime around 10 p.m., Spitzer sneaked away from his security detail and made his way to her room, the official said.
The officials spoke to the AP on condition of anonymity because of the sensitivity of the case.
According to an affidavit, a federal judge approved wiretaps on the escort service's telephone in January and February. FBI agents in Washington had the Mayflower under surveillance when Spitzer was in town, a senior law enforcement official told the AP.
In the court papers, an Emperors Club employee was quoted as telling Kristen that Client 9 - identified as Spitzer, according to investigators - might ask to do things "you might not think were safe," and Kristen responded by saying: "I have a way of dealing with that."
A law enforcement official said Tuesday the discussion had to do with Spitzer's preference not to wear a condom.
The poll released Tuesday indicated dissension among voters. Spitzer's approval rating was 30 percent, down from 35 percent in January. In November 2006, he won office with a historic 69 percent of the vote.
Even if Spitzer resigns, 49 percent of New Yorkers said he should face criminal charges.
The telephone poll conducted Tuesday surveyed 624 registered voters and had a margin of error of plus or minus 4 percentage points.
Spitzer has not been charged, and prosecutors would not comment on the case. Michele Hirshman, Spitzer's former deputy attorney general and now a member of a high-powered New York law firm, has been retained to represent the governor.
Action News, ABC News and The Associated Press compiled information for this report.