Players have to be waived by 11:59 p.m. ET Friday to become available for activation in the playoffs.
The Spurs announced the buyout Friday night.
"Pau Gasol is an exceptional individual and the ultimate professional," Spurs coach Gregg Popovich said. "We are grateful for his contributions on the court, in the locker room and in our community."
The move sets the stage for the Gasol brothers to compete in pursuit of the conference championship. Marc Gasol joined the Toronto Raptors (45-17) last month in a trade-deadline deal with Memphis. Milwaukee currently leads the Eastern Conference with a 47-14 record.
Gasol also will give the Bucks roster something it didn't have: championship experience. The roster has none. He's considered one of the better teammates and mentors in the NBA and won titles with the Lakers in 2009 and 2010.
Gasol, 38, saw his role diminish with the Spurs this season, partly due to him missing 26 games with a stress fracture in his foot. He was averaging career lows of 4.2 points and 4.7 rebounds in 12.2 minutes.
Gasol was guaranteed $6.7 million of his $16 million salary in 2019-20. He is earning $16 million this season.
"Today, I bid farewell to @spurs," he tweeted. "It's been a dream to play for 1 of most storied franchises in @NBA history, an honor to be part of Spurs family. To all the staff, my teammates, the coaches, RC, Pop and, above all, the fans, thank you for making this place so special. #GoSpursGo!"
Gasol has averaged 17.1 points and 9.2 rebounds during his 18-year NBA career.
ESPN's Malika Andrews contributed to this report.