In an interview, Mr. Spitzer, a Democrat, said that he believes he could make a big impact in the role, and is asking New Yorkers to give him a second chance.
"I'm hopeful there will be forgiveness, I am asking for it," he said in a telephone interview Sunday night.
His re-entry comes in an era when politicians —like Representative Mark Sanford of South Carolina and the New York mayoral contender Anthony D. Weiner — have shown that public disapproval, especially over sexual misconduct, can be fleeting, and voters seem open to those who seek forgiveness and redemption.
Mr. Spitzer, an aggressive watchdog over Wall Street when he served as attorney general, wants to overhaul the sometimes overlooked office into a more activist one, given the power the comptroller exercises over the city's pension funds and city spending.
"The metaphor is what I did with the attorney general's office," he said Sunday night. "It is ripe for greater and more exciting use of the office's jurisdiction."
The son of a wealthy real estate developer, Mr. Spitzer intends to pay for his campaign out of his own fortune, forgoing the city's public financing system.
Mr. Spitzer has little time to waste: To make the primary ballot in September, candidates for citywide office — mayor, comptroller and public advocate — must collect a minimum of 3,750 signatures from registered voters from their political party by Thursday.
With Mr. Spitzer's name recognition and three million Democrats in the city, this should not be a difficult task to complete, but he plans to flood the streets and supermarkets with some 100 signature gatherers starting Monday.
"I am going to be on the street corners," he said. "We will be out across the city."
Mr. Spitzer's entry promises to shake a comptroller's contest that, until now, had been viewed as a all-but-certain victory for Scott M. Stringer, the Manhattan borough president.
Mr. Spitzer resigned as governor on March 17, 2008, after The New York Times reported he had patronized a high-end prostitution ring called Emperors Club VIP.
