Police Commissioner Keechant Sewell announced Monday she was stepping down after nearly a year and a half at the helm of the NYPD, The Post has learned.

“Since I joined you almost a year and a half ago we have faced tremendous tragedy, challenges and triumphs together,” Sewell wrote in an email to the department Monday afternoon.

“I have witnessed your compassion, heroics and selflessness on a daily basis,” the email, obtained by The Post, read.

“They have reaffirmed to me what people around the globe have always known: you are an extraordinary collective of hard working public servants dedicated to the safety of this city, engaging our communities and sharing what we know with our partners for the benefit of the world,” Sewell wrote.

“Please continue to do what you do well to secure this city.”

Sewell, appointed by Mayor Eric Adams, was sworn in as the first woman to lead the NYPD on Jan. 1, 2022.