Spitzer also will collect petition signatures during the midday appearance in Union Square. Candidates for citywide offices like comptroller have to have 3,750 signatures from registered voters in their party by Thursday.
The Democrat, who stepped down in 2008 amid a prostitution scandal, has spoken in the past about the potential for the comptroller's job to look into corporate misdeeds. That would be similar to what he did as the state's attorney general, when he was known as the "sheriff of Wall Street."
Spitzer, a married father of three, has returned to public life as a commentator, with shows on CNN, Current TV and NY1.
He said he hoped city voters would give him a chance.
"I'm hopeful there will be forgiveness, I am asking for it," he told The New York Times, which first reported his run on Sunday.
Spitzer reiterated the theme Monday on WCBS television, saying he had "sinned," ''owned up to it" and hopes the public will judge him on his record in public service.
He said he'd discussed his potential run with his wife and daughters before making the decision over the weekend.
He conceded that getting back into politics under the circumstances will require "skin as thick as a rhinoceros."
Current Comptroller John Liu is running for mayor.
Manhattan Borough President Scott Stringer has been the most prominent among the contenders to become New York City's next fiscal chief. He's raised more than $3.5 million and spent about $566,000, city campaign finance records show, while his opponents have yet to report any fundraising or spending.
They include Republican John Burnett, who has worked on Wall Street in various finance capacities and just recently declared his candidacy; Green Party candidate Julia Willebrand, a former teacher; and former madam Kristin Davis. Davis once ran three escort services and claims to have provided hookers to Spitzer, which hasn't been proven.
Spitzer is not the only politician who's looking for a second chance.
Former Rep. Anthony Weiner is running for mayor. The former Democratic congressman left office two years ago amid a scandal over his tweets.