He played college basketball for the University of Illinois Fighting Illini before being selected by the Portland Trail Blazers with the 11th overall pick in the 2012 NBA draft.

His mother Tracie, once an athlete who would run upwards of 10 miles a day, had been largely housebound since her husband's death, due to an old horseback injury and subsequent disc surgery that left her with crippling pain.

Brian Siler, an insurance agent in Robinson who had a son of the same age, was aware of Leonard's family situation, and eventually became a father figure.

According to ESPN.com writer Dana O'Neil: "Looking to shoehorn the relationship into a convenient box, outsiders have called this Meyers' version of The Blind Side, but the comparison is inaccurate.

"[2]Leonard entered high school as a guard, but was converted to center after a six-inch (15 cm) growth spurt between his freshman and sophomore years.

Leonard led Robinson High School to the IHSA class 2A state championship[3] before choosing to play collegiate basketball at the University of Illinois.

[5] Leonard was one of 12 selected players that competed as Team USA in the 2011 FIBA U19 World Championships in Latvia from June 30 – July 10, 2011, and placed fifth in the competition.

[4] Leonard was named Big Ten Co-Player of the Week on December 5, 2011, after averaging 16.5 points and 6.0 rebounds per game in two Illinois victories.

[14][15] On October 31, 2012, Leonard made his NBA debut, logging 23 minutes and scoring four points against the Los Angeles Lakers.

[18] Leonard's numbers dipped from his rookie to sophomore season, falling behind fellow second-year big man Joel Freeland as the primary backup to starter Robin Lopez.

[20] In 2014–15, Leonard played only 13 total minutes in Portland's first 9 games as he was stuck in the big-man rotation behind Lopez, Freeland and Chris Kaman.

On November 15, 2014, with LaMarcus Aldridge scratched with an upper respiratory illness against the Brooklyn Nets, Leonard picked up the start at power forward, playing 29 minutes.

But when Lopez broke his hand going up for a rebound against the San Antonio Spurs on December 15, Leonard got another chance to show that he deserved time on the court.

[29] On May 20, 2019, in game 4 of the Western Conference Finals, Leonard recorded a career-high 30 points and 12 rebounds in a 119–117 overtime loss to the Golden State Warriors.

[33] On March 9, 2021, the Heat announced that Leonard would be suspended indefinitely while the NBA conducted an investigation into his use of an anti-Semitic slur during a Twitch video game livestream session.

[39] On January 13, 2023, the Los Angeles Lakers hosted Leonard for a workout, which was the first publicized activity of his attempted NBA comeback after his anti-Semitism controversy.

[51] On March 9, 2021, Leonard received criticism for using the antisemitic slur "kike" during a Twitch stream while playing Call of Duty: Warzone.