The "Men in Black" star portrays the tennis aces' family patriarch in the upcoming biopic King Richard and, speaking on "The Tonight Show Starring Jimmy Fallon", he admitted working on the movie was an eye-opener.
"What was really interesting to me is that, you know, we all feel like we have a picture of Richard Williams and it's the classic overbearing father hammering his children," said Will.
"But in sitting with Venus and Serena and their sisters and their mother, it was completely the opposite," he added. "He was a loving, caring, doting father."
"Venus referred to it as the 'Jedi mind trick' that he had somehow made it so they would have to ask him, 'Please, daddy. Can we play tennis?' Their punishment would be that they couldn't play tennis when they got in trouble."
"He aligned with what they wanted for themselves more than demanding what he wanted for them," he said.
The dad-of-three admitted studying the family ahead of the role was a real lesson for him as a parent, as well, insisting, "You want to be in alignment with your kids versus forcing and pushing and demanding."
"King Richard" hits cinemas on 19 November (21).
In the true-story movie, a young Serena Williams is played by Demi Singleton while her sister Venus is portrayed by Saniyya Sidney.