Details of the deal announced Friday weren't released.
Diaw had fallen out of favor with Bobcats coach Paul Silas, and his agent said he wanted to play for a contending team.
The Bobcats entered Friday with an NBA-worst seven wins, while the Spurs started the day second in the Western Conference at 30-14.
Charlotte acquired the eight-year veteran in a 2008 trade with Phoenix, and he started a franchise-record 258 games before getting benched earlier this month.
He was averaging 7.4 points and 5.3 rebounds for the Bobcats this season and has career averages of 9.6 points, 4.9 rebounds and 4.0 assists. He has a 13.9-point average in 39 playoff games.