The movie follows Williams’ career from his breakthrough in the 1940s to his death from heart failure, slumped in the back of his Cadillac, at the age of 29 in 1953.
London-born “Thor” actor, Hiddleston, said one of the biggest challenges he faced was learning Williams’ accent.
“He has a resonant tone of a gospel preacher, which comes from something deep in his southern roots,” he told Reuters at the film’s premiere in Los Angeles on Tuesday night. “As soon as I started to listen to the cadence and the musicality of the way he spoke, that was when it clicked for me.”
He described the singer-songwriter – whose hits included “Your Cheatin’ Heart” and “I’m So Lonesome I Could Cry” – as “a cornerstone in the development of American music”.
“Music is the most evocative, most immediately emotional art form, I think. My admiration for singers is huge and I think singing is the most naked means of expression, there’s nothing to hide behind,” Hiddleston said.
The film also looks at Williams’ relationship with his first wife Audrey, played by “Avengers” star Elizabeth Olsen, which grew more tempestuous as the singer relied increasingly on painkillers and alcohol.
It is one of several music biopics, including “Miles Ahead” with Don Cheadle as Miles Davis and “Born to Be Blue” in which Ethan Hawke portrays Chet Baker, to be released this year.
“I Saw the Light” opens in cinemas in Los Angeles, New York and Nashville on Friday.