The nonprofit group that raised millions of dollars to advance Mayor Bill de Blasio’s political agenda — using what a government watchdog denounced last month as “dark money” — said Thursday it is preparing to close.

The Campaign for One New York, which is not subjected to the same stringent disclosure rules as traditional political campaigns, will stop fundraising, de Blasio said.

“The work is done,” de Blasio told reporters at the city’s St. Patrick’s Day parade. “The Campaign for One New York was created to address income inquality.”

The group ushered in a “success” on his universal pre-K rollout and is “on the verge of a great victory” with his affordable housing plan set to win passage in the City Council, the Democratic mayor said.

The 501 (c4) organization, which started at the tail end of de Blasio’s 2013 mayoral campaign — raised about $4.4 million in 2014 and 2015, according to records it voluntarily disclosed on a biannual basis.

Its donors included members of the yellow taxicab industry, real estate developers, advocates of a ban on Central Park’s horse-drawn carriages and others who had or wanted business before the city.

Good-government group Common Cause/New York last month requested a probe into the nonprofit’s dealings, saying it spawned a “shadow government that raises serious questions about who has influence and access to the policymaking process.”

Executive director Susan Lerner applauded the closure.

“Common Cause/NY does not accept that secret money is a necessary function of the modern mayoralty,” she said, adding that the setup serves “only to breed mistrust and confusion among voters.”

A second nonprofit linked to de Blasio, called United for Affordable NYC and formed to promote his housing blueprint, is also set to close once the associated bills pass the City Council, the group said Thursday.

— With Matthew Chayes

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