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.