An NYPD sergeant who helped expose the karaoke-bar corruption scandal in Queens’ 109th Precinct has filed a suit that claims he’s being wrongly punished for blowing the whistle on his fellow cops.

Steven Lee says in court papers that current and former NYPD officials have engaged in a “persistent campaign to harass, defame, threaten, intimidate, extort and endanger [his] life.”

The Queens Supreme Court filing seeks unspecified damages on grounds including illegal retaliation under the state’s Civil Service Law and “intentional infliction of emotional distress.”

In a notice of claim against the city last year, Lee demanded $35 million.

His suit, filed electronically Saturday, includes a letter in which the Queens District Attorney’s Office last year praised Lee’s “remarkable” undercover work that led to the corruption convictions of former NYPD Lt. Robert Sung and Detective Yat Yu Yam.

The two officers were accused of overlooking alleged drug sales and prostitution in two karaoke bars in exchange for kickbacks. They eventually copped to no-jail plea deals.

Lee’s suit claims he’s also “uncovered a myriad of evidence of widespread corruption at high levels of the NYPD” and says former Police Commissioner Bill Bratton — who’s named as a defendant — “may also have been involved.”

But the NYPD’s Internal Affairs Bureau “denied [Lee’s] requests to continue the investigation, and instead considered the matter closed,” court papers say.

Lee also says he’s been told that he’s about to be slapped with departmental charges for missing an “interrogation” that his boss told him had been canceled, which his suit calls “clearly a bogus trap.”

Lee’s lawyer, former cop Joseph Murray, said he was sending copies of the suit to Mayor Bill de Blasio and other top city officials “to demand hearings on the pervasive corruption that is being suppressed by the NYPD.”

The NYPD referred questions to the city Law Department, which said, “We will review the complaint.”