In a letter submitted to the San Antonio Express-News, Leonard thanked the Spurs organization, his former teammates, coach Gregg Popovich and the team's fans.
"I have been going back and forth the last few weeks trying to figure out the right things to say, and it comes down to two simple words: THANK YOU!" Leonard wrote.
Leonard's exit from San Antonio had been tumultuous. He appeared in nine games for the Spurs in 2017-18, last playing on Jan. 13 before sitting out the rest of the season with a quad injury.
Spurs doctors had cleared Leonard to return to play last season, but he sought second opinions and did not return, making his health a question mark following the trade. But he passed a physical to make the deal official.
In his letter, Leonard praised Popovich, saying he will "always be grateful for my growth under your guidance."
Leonard was a two-time All-Star in seven seasons with the Spurs. He was the Finals MVP in 2014 when the Spurs beat the Miami Heat in five games for the title.
"Through all the ups and downs -- I'm glad there were many more ups! -- I'll never forget what we have shared and accomplished together," Leonard wrote.
"While I'm looking forward to the next chapter in my career, I'll always remember the city and the people of San Antonio!"