Williams was found dead in his New York City apartment Monday afternoon, a law enforcement official told CNN.
Investigators found drug paraphernalia near his body, the official said. The investigation is ongoing, according to another law enforcement source who spoke to CNN.
CNN has contacted representatives of Williams for comment.
Williams, a Brooklyn native, most recently appeared in HBO’s “Lovecraft Country” and the series “F Is for Family.”
He became an almost iconic figure for many thanks to his role in “The Wire” as Omar Little, a shotgun-wielding character who made his living robbing drug dealers. He followed that up as a mobster in the HBO Prohibition-era mob drama “Boardwalk Empire,” and most recently earned an Emmy nomination for another series on the pay network, the macabre “Lovecraft Country.”
Williams was next slated to co-star in Sony’s George Foreman biopic from George Tillman Jr., who was set to direct.
Williams amassed a number of accolades during his storied career, including five Emmy nominations. His first was in 2015 for his role in “Bessie” and another followed two years later for his part in “The Night Of.”
He was also the winner of a SAG Award for best ensemble with the cast of “Boardwalk Empire.”
On social media, Williams’ many colleagues and friends recalled the depth, complexity and humanity he brought to his characters on screen and, above all, the man he was off screen.
Director James Gunn added: “Michael K Williams, in addition to being one of the most talented actors around, was also one of the kindest, sweetest, most gentle souls I’ve ever met. This is heartbreaking. My thoughts are with all those who loved him.”
CNN’s Brian Lowry and Marianne Garvey contributed to this report.