The 66-year-old billionaire businessman, who aides had said was prepared to spend $1 billion to run as an independent, wrote in an editorial on The New York Times' Web site that he will work to "steer the national conversation away from partisanship and toward unity; away from ideology and toward common sense; away from sound bites and toward substance."

Bloomberg, who has almost two years left in his second term at City Hall, had publicly denied any interest in running for president since one of his political advisers first planted the seed more than two years ago.

But his denials grew weaker in recent months as aides and supporters quietly began laying the groundwork for a third-party campaign. Read More