"New Yorkers know first hand how effective Hillary is as a leader, which is why her support runs deep in this state," Spitzer said Tuesday. "As senator she has capably represented New Yorkers and together with countless other supporters I look forward to sharing with the rest of the country the values and strengths that will make her an excellent president."
Spitzer had thus far put off an endorsement, saying it was premature.
The event Monday is expected to draw a host of other New York Democrats, including state Attorney General Andrew Cuomo and Lt. Gov. David Paterson.
For months, Spitzer has hedged about an endorsement of Clinton, who leads national polls for the Democratic nomination. But the governor had dropped enough hints that the endorsement really came down to a guessing game about when — not if — it would happen.
"What an amazing president she will be for every person in this country," Spitzer gushed last month when the two spoke before a teachers' convention in Washington.
New York Democrats have generally lined up behind Clinton with a few exceptions: state Sen. Bill Perkins, a former New York City Council member, recently endorsed Sen. Barack Obama's presidential bid.