Financial terms were not disclosed.
Rondo averaged 10.6 points and 5.1 assists last season, when the Celtics' won their 17th NBA championship. The former Kentucky Wildcat is entering his third season in the NBA and second year as a starter in Boston.
The 6-foot-1 guard was acquired by the Celtics in a draft-night trade from the Phoenix Suns. He had 14 points and six assists in Boston's season-opening win over Cleveland on Tuesday.
Information from The Associated Press was used in this report.