The Mavericks used their entire midlevel exception in their second free-agent deal with Diop since 2005.
A lottery pick in Cleveland, Diop struggled before joining Dallas. He combined with Erick Dampier at center when the Mavericks reached the NBA finals in 2006 and won a franchise-record 67 games the next season.
Diop averaged 2.5 points and 5.1 rebounds in 214 games, including 72 starts, with Dallas.
The Mavericks on Wednesday also announced the re-signing of guard J.J. Barea. The team did not disclose terms of its deal with Barea, who spent each of the past two seasons with Dallas.
Barea played in 44 games last season, starting nine times. He averaged 4.3 points and 1.3 assists and made nearly 39 percent of his 3-pointers.
"J.J. has worked extremely hard and has developed into a fine young NBA point guard," said Donnie Nelson, team president of basketball operations.