The seventh-year swingman agreed to a one-year, $2.5 million contract, his agent, Mark Bartelstein, confirmed to ESPN.com last Thursday.
The team announced Monday that it had signed the 6-foot-6 Daniels after his disappointing first season with the club. The seven-year veteran missed 28 games with a torn ligament in his left thumb that required surgery and averaged a career-low 5.6 points in 51 games.
In the Celtics' last 25 games, Daniels sat out two, scored two points seven times and was held scoreless six times.
He played in only 11 of the team's 24 playoff games and just two of the seven games for a total of 4 minutes, 21 seconds in the NBA finals won by the Los Angeles Lakers. In 2008-09 he averaged career-highs of 13.6 points and 4.6 rebounds in 54 games with the Indiana Pacers.
Information from The Associated Press contributed to this report.