The actor was found dead Monday afternoon in his Brooklyn apartment, the New York City Police Department confirmed to USA TODAY.
Williams appeared on many HBO series, including “The Wire,” “Boardwalk Empire,” “The Night Of” and most recently, “Lovecraft Country.”
The actor's films included “Inherent Vice,” “12 Years a Slave,” “Gone Baby Gone” and “The Road.”
Throughout his career, Williams received five Emmy nominations, four of them for outstanding supporting actor.
“I was playing with fire,” Williams told the news outlet at the time. “It was just a matter of time before I got caught and my business ended up on the cover of a tabloid or I went to jail or, worse, I ended up dead.”
And when he decided to get clean, Williams wondered whether surviving it all was pure luck.
“I thought, ‘Why me? Why did I get spared?’ I should’ve been dead,” Williams said. “I have the scars. I’ve stuck my head in the lion’s mouth. Obviously, God saved me for a purpose. So, I decided to get clean and then come clean. I’m hoping I can reach that one person.”
Celebrities took to social media Monday to pay tribute to the late actor.
"The Wire" actor Isiah Whitlock Jr., who played State Senator Clay Davis on the HBO series, wrote he was “shocked and saddened” by Williams' death.
“One of the nicest brothers on the planet with the biggest heart,” he wrote. “An amazing actor and soul. May you RIP. God bless.”
Tray Chaney, who also starred in "The Wire," wrote he was "crushed."
"No words. I love you bro. RIP to the legend Michael K Williams aka one of the dopest Actors/Brother in the world," Chaney tweeted. "#Omar #TheWIRE FOR LIFE. I'm off the grid for a while to process this one. I love you bro smh damn."
Alec Baldwin fondly remembered the time he had the "pleasure of working" with Williams on Emilio Estevez's film "The Public."
"He was … is … a startlingly raw and powerful actor. Rest In Peace," he wrote.
Director James Gunn wrote that "in addition to being one of the most talented actors around," Williams was "also one of the kindest, sweetest, most gentle souls I've ever met."
"This is heartbreaking," Gunn added. "My thoughts are with all those who loved him."
Director Travon Free remembered the late actor as a "genius, a black queer icon who challenged the ideas of black masculinity at a time when it wasn't easy" and as a "truly great dude."
Born in Brooklyn on Nov. 22, 1966, Williams was raised in the Vanderveer Projects in East Flatbush.
This story is developing.
If you or someone you know is struggling with substance abuse or addiction, you can call the Substance Abuse and Mental Health Services Administration National Helpline at 800-662-HELP (4357) any time of day or night.