On February 18, Sizemore collapsed in his Los Angeles home and was transported to the hospital by paramedics. There, doctors determined that he had suffered a brain aneurysm as the result of a stroke.
Sizemore had remained in critical condition since then and had been in a coma under intensive care.
"I am deeply saddened by the loss of my big brother Tom," his brother Paul Sizemore said in a statement.
"He was larger than life. He has influenced my life more than anyone I know. He was talented, loving, giving and could keep you entertained endlessly with his wit and storytelling ability. I am devastated he is gone and will miss him always."
Born in Detroit on November 29, 1961, Sizemore moved to New York City to pursue acting in the '80s. One of his first credits came in 1989 with an appearance in Oliver Stone's best picture nominee 'Born on the Fourth of July'.
Known for playing the tough guy, he rose to fame in the 1990s with films like 'Harley Davidson and the Marlboro Man', 'Passenger 57','True Romance' and 'Natural Born Killers'.
He got his big break in Steven Spielberg's 1998 war film 'Saving Private Ryan', in which he played Technical Sergeant Mike Horvath. 'Saving Private Ryan' went on to score a best picture nomination at the Academy Awards. Along with his co-stars, among them Tom Hanks and Matt Damon, Sizemore received a Screen Actors Guild nomination for outstanding performance by a cast in a motion picture.
Over the course of his career, Sizemore has worked with directors including Michael Mann, Martin Scorsese, Peter Hyams, Carl Franklin, Oliver Stone, Ridley Scott and Michael Bay.
Sizemore was also a convicted abuser. In 2003, he was convicted of domestic violence against his girlfriend at the time, and in 2017, Sizemore pled no contest to two charges of domestic violence after being arrested a few months earlier on suspicion of assaulting his partner.
In 2005, Sizemore was sentenced to several months in jail after being caught attempting to fake a urine test. In 2007, he was arrested for possession of methamphetamine, and in 2019, he was arrested for possession of "various illegal narcotics."
Sizemore has been public about his struggles with substance abuse, appearing on 'Celebrity Rehab With Dr. Drew' and 'Dr. Phil' to discuss his legal troubles.
In 1998, the actor shared that his 'Heat' and 'Witness to the Mob' co-star, Robert De Niro, personally assisted in helping Sizemore enter a drug rehabilitation programme. In 2013, the actor released a memoir detailing his career and personal battle with addiction, titled 'By Some Miracle I Made It Out of There'.
Sizemore is survived by his two children, Jagger and Jayden. There will be a private cremation service for Sizemore's family, with a larger celebration of life event planned in a few weeks.