News of the star’s sudden death has shaken fans of HBO TV series, The Wire and Boardwalk Empire, for which the 54-year-old actor was best known.
Williams, who memorably played shotgun-wielding stick-up man Omar Little on HBO's acclaimed crime drama, was found dead at his home in Brooklyn on Monday, police in New York said.
A representative confirmed the news, describing the death of Williams as an "insurmountable loss".
He was a four-time Emmy nominee for Bessie, The Night Of, When They See Us and Lovecraft Country.
As well as The Wire, Williams, who had a distinctive facial scar from a bar fight on his 25th birthday, had roles in gangster series Boardwalk Empire and TV film Bessie.
Last week it was announced Williams had joined the cast of Sony's untitled biopic of famed world heavyweight champion George Foreman.
He was set to play Doc Broadus, who was Foreman's trainer and mentor.
Here’s what you need to know about Michael K Williams, his TV and film career and the cause of his sudden death.
Who was Michael K Williams?
Williams, born and raised in Brooklyn, New York, rose to prominence after first starring in music videos as a dancer before landing a role as a drug dealer in Martin Scorsese's 1999 drama film Bringing Out The Dead.
He went on to play a small part in The Sopranos - a show alongside The Wire perennially discussed as being the best ever - before he appeared as Omar in 2002.
In 2015, Williams told The Guardian: “I use my job to engage empathy and compassion for people society might stereotype or ostracise”.
“No one wakes up and says ‘I’m going to become a drug-dealer’ or ‘I’m going to become a stick-up kid’.
"No. There is a series of events that makes them feel this is the only way out.
Williams added: “As a black man growing up in the hood, I bear witness to some of those events.”
Williams, who was born and raised in East Flatbush, Brooklyn, looked back on a tough upbringing during a 2017 interview with the New York Times.
He revealed he had been molested as a child and developed a drug addiction.
"The characters that mean the most to me are the ones that damn near kill me," Williams said of his gangster roles which caused old trauma to resurface. "It's a sacrifice I've chosen to make."
While he did not identify as gay, Williams revealed he felt a sense of belonging in the Manhattan gay bars of the 1980s and 90s.
He was scarred for life in a bar fight in Queens.
The New York Times said he intervened to stop a group of men jumping his friend, only to have his face and neck sliced with a razor blade.
It left a distinguishing scar from the top of his forehead to the middle of his right cheek, which became an indelible part of his acting career.
What was Michael K Williams’ cause of death?
So far, William’s official cause of death has not been provided.
The death is being investigated by the New York City medical examiner, but reports from US media have suggested that his death is being investigated by New York City Police as a possible drug overdose.
These reports have not been officially confirmed, however.
Which stars have paid tribute to Michael K Williams so far?
Spike Lee, Wendell Pierce and Aldis Hodge have led the tributes to The Wire actor Michael K Williams following his death aged 54.
Pierce, 57, starred alongside Williams on The Wire, playing Detective Bunk Moreland.
He wrote a moving Twitter thread and said: "The depth of my love for this brother, can only be matched by the depth of my pain learning of his loss. A immensely talented man with the ability to give voice to the human condition portraying the lives of those whose humanity is seldom elevated until he sings their truth."
Fellow star in The Wire, Lance Reddick also paid tribute to Williams on Twitter, calling the 54-year-old Boardwalk Empire actor “one of the kindest, gentlest, most genuine, giving and courageous souls I've ever met.”
Reddick, who played Colonel Cedric Daniels on the landmark crime drama series, added: “Rest in peace, my brother.”
He was joined by fellow actors leaving scores of tributes to Williams on social media, with Hollywood actress Mia Farrow tweeting: “We have lost another irreplaceable actor.
"RIP Michael K.Williams.
"You were too young to leave us- we were looking forward to so many more great performances.
"Thoughts with family and friends.”
Additional reporting by PA Los Angeles Correspondent Keiran Southern