Mayor Bill de Blasio violated ethics laws when he hit up fat-cat donors with business before city agencies as he raised $4 million for his nonprofit created to tout his accomplishments.

The explosive findings come from a heavily redacted summary of a now-closed Department of Investigation examination into Hizzoner’s fundraising practices from which no charges were brought.

DOI investigators reported they “substantiated” reports the “Mayor solicited contributions from any individual who had, or whose organization had, a matter pending or about to be pending before any executive branch of the City.”

All of the other conclusions and recommendations from the 15-page report into the fundraising at the Campaign for One New York were redacted.

The Post obtained the document under the state’s Freedom of Information Law late Wednesday.

Non-profit news outlet The City first revealed its existence.

City ethics laws forbid officials from soliciting individuals or companies with business pending before agencies to donate to nonprofits that boost the official’s message, like the Campaign for One New York.

The non-profit was initially founded to boost de Blasio’s universal pre-kindergarten program but later expanded to boost his overall political ambitions.

It fell into the crosshairs of Manhattan and federal prosecutors, who eventually declined to prosecute de Blasio over his fundraising practices but blasted Hizzoner for violating the spirit — if not the letter — of the law.

DOI interviewed four separate developers — identities all redacted — that had business before de Blasio appointees as Hizzoner tried to grease them to donate to his nonprofit.

Hizzoner told investigators in all four cases he either did not remember speaking to the developers or “remembered no details of the communication,” the DOI summary reported.

Unnamed Developer A told investigators they had business before three city agencies when they met with Hizzoner and an unnamed staffer for 20 minutes in February or March 2015, where the staffer spoke about raising money for the Mayor’s priorities. Records show that Developer A cut the Campaign for One New York a check in March 2015.

In a second case, Developer C cut two checks to the Campaign for One New York — in February 2014 and April 2015 — while having business pending before the city.

Additionally, city ethics laws require officials to tell donors that any decision “whether or not to give will not result in official favor or disfavor.”

All of the developers said de Blasio never made the statement.

DOI’s October 2018 investigative summary also exposed that de Blasio’s nonprofit raised $1.37 million before ever adopting a written policy that governed which companies and individuals de Blasio could legally solicit.

The non-profit’s policy claimed that while Hizzoner “may not solicit funds from any individual or entity that has ‘matters pending or about to be pending before any city agency,’ it also said that de Blasio may ‘encourage excitement and support for [universal pre-K — CONY’s original purpose] with individuals who have matters pending.’ ”

De Blasio’s fundraising practices are under intense scrutiny once again as he toys with a possible 2020 presidential bid.

He attended a Boston fundraiser for his political operation — Fairness PAC — that was hosted by Beantown’s top developer, John Fish, earlier this month.

Fish’s firm, Suffolk Construction, is actively pushing to expand its presence in New York City and hired de Blasio’s disgraced former Housing Authority chairwoman Shola Olatoye last year to help lead the effort.

While Fairness PAC is paying for de Blasio’s tour of the early presidential states, it is not required to report its donors until July.

“These questions are asked and answered,” said Freddi Goldstein, City Hall’s top spokeswoman. “Fundraising for the now-defunct Campaign for One New York was thoroughly reviewed by multiple parties and it was determined that there was no wrongdoing. It’s been said a million times: the Mayor acted lawfully and ethically.”