The Colts defensive leader wrote in a Tweet that the procedure "went well" and that he's "ready to get back going!"
Leonard is expected to miss the start of training camp, coach Frank Reich said Tuesday.
"He's had a back issue that has been a progressive thing that started early in the offseason, but has been something that has progressed," Reich said. "We recently made the evaluation that he's going to have a procedure on his back [Tuesday]. Miss some training camp time, but if all goes according to plan, he should be ready for the start of the regular season."
Leonard's back surgery adds to what's already been a frustrating offseason for the three-time All-Pro linebacker. He's yet take part in on-the-field work so far with the team while recovering from a lingering ankle injury that bothered him all of last season.
Not having Leonard on the field made it difficult for the Colts to understand how significant his back problem has been.
"The best of my understanding is that early in the offseason, something was not feeling right," Reich said when asked about Leonard's injury just coming to light. "Let's keep an eye on it, not overreact, and it kind of got worse rather than better. But since he wasn't practicing you don't know that because of the ankle."
Reich also added, "I'm not the back expert either. So at some point we'll likely come out with a clear statement. Very optimistic about the procedure."
Leonard has been one of the premier defensive players in the NFL since entering the league as a second-round pick in 2018. He is the only player in NFL history with 10 or more interceptions (11), 15 or more sacks (15), and 15 or more forced fumbles (17) in the first five years of his career. Leonard is just entering his fifth season in the NFL. E.J. Speed has been working at Leonard's spot at linebacker in his absence.
"With Darius, don't know the exact timetable of the return in my mind as long as he's ready for the regular season," Reich said.