The "One Night in Miami..." star plays a gangster in the film, which focuses on a young Tony Soprano, played by James Gandolfini's son, Michael Gandolfini, but the "Hamilton" star's audition was so secretive that he didn't know what he was trying out for at first, and producers didn't let him see the script.
"I'd heard that the film was happening. I wasn't up for it in the original rounds of auditions. But there came a point where they needed someone quickly, and I got the call," Leslie told Rolling Stone magazine.
"I don't even know that I knew I was auditioning for the Sopranos [movie]. They keep things very tight to the vest. They're like the MCU [Marvel Cinematic Universe]. They don't send you a script, don't send you character names, scenarios are changed. You have to make some choices as an actor. You take what you see, and you start inventing."
"I got a call that they liked the tape that I made, but they had some notes for me. I taped again, then they wanted me to tape again with more notes. And I said, 'Guys, I don't mind taping again, but you've got to send me a script. I don't know what I'm doing'."
He eventually learned he was trying out for Harold McBrayer - a small-time numbers runner with big ambitions, who works for Tony Soprano's uncle Dickie Moltisanti, played by Alessandro Nivola.