Perkins will receive almost $36 million fully guaranteed over the course of the four-year contract, his agent, Bob Myers, told ESPN The Magazine's Ric Bucher.
"We had a unique opportunity to enter into discussions with Kendrick to solidify his future with our organization," general manager Sam Presti said in a statement. "We are pleased to know that he will be a part of our core group now and in the future. Kendrick's blue-collar, team-first approach aligns with the vision we hold for building a sustainable team in the Oklahoma City community."
The 26-year-old Perkins was unable to agree to an extension with the Boston Celtics, who dealt him to the Thunder at the trade deadline for starters Jeff Green and Nenad Krstic. Guard Nate Robinson also came over to Oklahoma City, which sent the Celtics a 2012 first-round draft pick and cash.
The Celtics had reportedly offered him a four-year, $22 million contract.
As part of the deadline deal that sent Perkins to Oklahoma City, the Thunder trimmed a tiny bit of cap space (a little more than $1 million), which gave them just enough additional wiggle room to help hammer out a contract extension. With Boston over the salary cap, the team couldn't offer more than $22 million over four years, while Oklahoma City was able to use that sliver of cap space to offer Perkins as much as $13 million more on a four-year deal.
Perkins said he was interested in playing for Oklahoma City as early as last offseason, when he discussed with agent Arn Tellem whether the Thunder might be interested in him when this season was over. He ended up moving sooner than he expected, and was initially shaken up at being traded away from the only NBA team he'd ever played for.
"It kind of felt like the worst day of my life when I got traded from the C's, from being there so long. But when I got here, it kind of took my mind away from everything, I think, and everything just kind of blew me away," Perkins said after practice Tuesday. "It was kind of the worst but best day."
Perkins, who has a sprained left knee, hasn't yet made his debut for the Thunder but said recently that he's hopeful he can be back in time for the Thunder's six-game homestand that starts March 18.
In 12 games with the Celtics this season, Perkins averaged 7.3 points and 8.1 rebounds.
The 6-foot-10 Perkins was the 27th overall pick in the 2003 draft.
Information from ESPNBoston.com's Chris Forsberg and The Associated Press was used in this report.