Retired detective John Cuddy, a longtime police investigator whose career in the NYPD helped bring down the “French Connection” heroin operation and Harlem gangster Nicky Barnes, died early Sunday morning in Suffolk County. He was 92.

“He was an honest guy,” said his son John, also a retired NYPD detective. “Those who worked with him knew him as Gentleman Jack.”

Cuddy started his career as an NYPD cop in the 108 precinct in Queens in the early 1950s, John told the Post on Sunday.

He earned a reputation as a hard-working cop, and in two years he was promoted to the NYPD’s narcotics division.

On the narcotics squad, Cuddy spent years rooting out heroin from opium dens in Chinatown in the late 1950s — and worked with other noted detectives, including Kitty Barry and John Kai.

But his largest case came after he had been promoted to sergeant and was supervising narcotics detectives.

In 1961, under Cuddy’s supervision, detectives Eddie Egan and Sonny Grosso broke up an international heroin ring and seized more than a hundred kilos of the drug. The case went on to be immortalized in the “French Connection” movie and book, with Egan being portrayed by Gene Hackman.

In 1971, Cuddy retired from the NYPD and took a job as an investigator with the Nassau County district attorney’s office — but his penchant for landing big cases didn’t stop.

In the 70s, Nassau County police arrested a Harlem man on a small charge, Cuddy’s son said. But because of a lengthy rap sheet, the man was facing prison time after the arrest.

Cuddy learned the arrested man was connected to Harlem drug kingpin Nicky Barnes and flipped him, John said. The informant helped bring a case against Barnes, who would go on to spend decades in prison.

Cuddy, who was also a charter member of the NYPD Emerald Society, died due to complications of old age. John Cuddy and other family members are organizing funeral arrangements.