After four years at the NYPD, Deputy Commissioner of Legal Matters Larry Byrne is stepping down, he told The Post.

“After four special years for me at the NYPD, I am sadly leaving the Department at the end of July to return to the private sector,” Byrne said Tuesday.

Byrne, whose NYPD police officer brother was shot and killed in the line of duty in 1988, said he had told his boss Police Commissioner James O’Neill about his decision.

Police Commissioner Bill Bratton appointed Byrne, who has worked both as a federal prosecutor and in private practice, to the position in July 2014.

He joined the US Attorney’s Office for the Southern District of New York as an assistant US attorney in 1988 and became deputy chief of the Organized Crime and Racketeering Section in the Department of Justice’s Criminal Division.

That was the same year Byrne’s brother, Officer Edward Byrne, was shot and killed outside a Queens home while protecting an immigrant witness who agreed to testify against drug dealers. Officer Byrne was only 22.

Former Deputy Commissioner for Public Information Stephen Davis responded to the shooting when Byrne’s brother was killed and has been friends with him through the years.

“Larry Byrne is one of the smartest guys that I have ever met in or out of the police department,” Davis said.

Davis said he wasn’t sure Byrne, a private lawyer at the time, would take the post when he was asked four years ago.

“He did it in a heartbeat for his family’s legacy,” Davis said. “Larry did this because of the legacy of his family, not only his brother but for his dad and his other brother who’s an FBI agent.”

Byrne, who’s dad was also an NYPD cop for 22 years, worked to create the Edward Byrne Memorial Justice Assistance Grant Program, which provides federal criminal justice funding to police agencies.