His manager, Dennis Aspland, confirmed Forman's death to The Hollywood Reporter and noted that the filmmaker had a home in Warren, Connecticut.
Forman is survived by his wife, Martina Zborilova-Forman, and four children.
He first attracted worldwide attention with features like Black Peter, The Loves of a Blonde(1965) - an Oscar nominee for best foreign-language film, and The Firemen's Ball.
Black Peter, his first major feature in 1964, won Forman global acclaim and his star only continued to rise with "Loves of a Blonde".
In 1968, he moved from what was then Czechoslovakia to the United Sates after Warsaw Pact troops invaded the country to crush the "Prague Spring".
When Soviet tanks rumbled into Prague in August 1968, Forman was in Paris for negotiations on his first American production and was sacked by his Czech studio, leading him to emigrate.
The Fireman's Ball was released in 1967 and Forman was then invited to the U.S. by Paramount Pictures to make a film in America.
Forman helmed the adaptation of Ken Kesey's novel "Cuckoo's Nest" and it went on to become a critically acclaimed film in 1975.
Miloš Forman, who rose to prominence as a key figure in the Czech New Wave before establishing himself as one of Hollywood's most sought-after directors, has died at 86.
The director, who worked meticulously, spending months with screenwriters and overseeing every aspect of production, didn't release another film until 1979's "Hair". But by the time it came out, America's brief period of student revolt had long since faded, and the public wasn't interested. Forman told Los Angeles Times in a 2004 interview. Both claiming the award for Best Picture.
Hunting for locations, Forman realized Prague was the only European capital that had changed little since Mozart's time, but returning there initially filled him with dread.
He was orphaned after his parents were taken to concentration camps. He had been in Paris when the communists crushed the Prague Spring movement in 1968, and he hadn't bothered to return home, becoming a USA citizen in 1975.
He returned to still-Communist Prague in 1983 to film Amadeus, which earned him a second Oscar and which won eight out of 11 nominations.
"There was an enormous affection for us doing the film", he remarked in 2002. It was nominated for, and won, multiple Oscars, including Best Picture.
Forman (c.) directed Danny DeVito (l.) and Jim Carrey (r.) in the Andy Kaufman biopic "Man on the Moon".
Forman's first wife was actress Jana Brejchova. With the latter he had twins boys, Matej and Petr, before leaving Czechoslovakia.