The deal also generated a trade exception for the Thunder.
Leonard will not be an active part of the Thunder moving forward and will not report to Oklahoma City, the team said in its statement announcing the deal.
Ariza, 35, delivers Miami a versatile and accomplished wing player for its Eastern Conference playoff push. Ariza hasn't played a game in a year, opting out of the Orlando restart for family considerations as a member of the Trail Blazers.
Leonard, whom the NBA fined $50,000 for an anti-Semitic slur last week, had to waive the no-trade clause on his two-year contract, which included a team option for 2021-22 -- that will be declined as part of a procedural matter in completing the deal.
Leonard, who had season-ending shoulder surgery in February, was agreeable to facilitate the deal as a gesture of good faith to the Heat organization, where he has played since arriving in a trade from Portland in 2019.
The key to the deal for Oklahoma City was stockpiling another future draft pick. Oklahoma City traded for another 2027 second-round pick last week in a deal with Detroit. Oklahoma City has accumulated 17 first-round picks and 15 second-round picks through the 2027 draft. The expectation is that Oklahoma City will keep Leonard under contract through the March 25 trade deadline in case there's opportunity to use his contract in another transaction, sources said.
Since his comments on March 8, Leonard has been working with the Jewish community in South Florida, sources said. He will continue rehabilitating his shoulder and training in the area.
Oklahoma City acquired Ariza as part of a three-team offseason deal with Detroit and Dallas. In a single week, Ariza was traded from Portland to Houston to Detroit to Oklahoma City.
Ariza is on a $12.8 million expiring contract.
After starting the season with Sacramento a year ago, Ariza was traded to the Trail Blazers, where he averaged 11 points and 4.8 rebounds in 21 starts. Ariza has averaged 10.5 points, 4.8 rebounds and 2.2 assists for his career in 16 seasons.