The 10-time All-Star forward formally signed with the team on Friday after spending last season with Washington, with which he averaged 11.9 points, 4.0 rebounds and 2.0 assists while starting 73 games.
He reportedly agreed to a $10 million, three-year deal after turning down the Wizards.
The Clippers signed Wesley Johnson on Thursday, which could lessen Pierce's minutes throughout the season.
Pierce starred at nearby Inglewood High before playing three years at Kansas and then being drafted 10th overall in 1998.
He helped Boston win the 2008 NBA title and was named MVP of the Finals when Rivers was coaching the Celtics.
The 37-year-old will spend the final years of his career playing in front of his hometown fans. He has averaged 20.7 points, 5.8 rebounds and 3.7 assists during a career that also includes a stint with Brooklyn. Pierce is 16th in NBA scoring with 25,899 points.
Rivers recruited Pierce as part of the group that visited DeAndre Jordan in Houston on Wednesday, when the big man reneged on his verbal agreement to join the Mavericks and decided to re-sign with the Clippers.
Although Pierce is new to the Clippers, Rivers said his 18 years in the NBA made him relevant in that situation.
"He was great," Rivers said Thursday. "He's always been pretty straightforward and a team builder."