Ryan Koss of Dorset, Vermont, was charged with "grossly negligent operation with death" after he turned into Williams' path as the actor was riding a motorcycle on June 12, according to Vermont State Police.
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Investigators said Koss attempted to turn left into a parking lot.
The initial investigation indicated the Honda Element driven by Koss stopped, signaled a left turn, and then turned into the path of the motorcycle, authorities said. Police said Williams was unable to avoid the crash and was thrown from his motorcycle.
He suffered critical injuries and was airlifted to Albany Medical Center in Albany, New York, where he was pronounced dead.
Treat Williams, actor known for role in 'Hair,' killed in motorcycle accident at 71
According to state police, the medical examiner's office in New York determined that Williams died of "severe trauma and blood loss as a result of the crash."
Police said investigators contacted Koss Tuesday evening. He voluntarily met with troopers at a local state police station where he was processed and later released.
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Koss' arraignment is set for Sept. 25.
Born Richard Treat Williams in Rowayton, Connecticut, the actor's versatile screen career included an early role in director Milos Forman's adaptation of the musical "Hair" in 1979, followed by a starring vehicle with another A-list director, Sidney Lumet, in the gritty undercover crime drama "Prince of the City" two years later.
While Williams appeared destined for major stardom, his next several movies didn't equal that early promise, though he continued to work steadily, including in a TV movie remake of "A Streetcar Named Desire" and additional TV movies in which he played boxer Jack Dempsey and FBI chief J. Edgar Hoover.
In the '90s, the actor segued into different kind of roles, playing the villain in the pulp-comic adaptation "The Phantom" and super-agent Michael Ovitz in the HBO movie based on the book "The Late Shift," about "The Tonight Show" succession battle between Jay Leno and David Letterman. He earned a Primetime Emmy nomination for that role.
Later in that decade, Williams enjoyed leading action star status in 1998's B-movie "Deep Rising," about a killer sea monster, starring opposite Famke Janssen, Wes Studi and Djimon Hounsou.
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Williams subsequently found new success in television, starring in the CW series "Everwood" for four seasons in the aughts and a more recent stint on "Chicago Fire." He was also part of the core cast of "Chesapeake Shores," appearing in 53 episodes between 2016 and 2022. He last year also co-starred in the HBO miniseries "We Own This City," producer David Simon's chronicle of corruption and internal politics in the Baltimore police department.
The late actor is survived by his wife Pam Van Sant and their two children.
CNN contributed to this report.