TORONTO, ON - OCTOBER 26: Aron Baynes #12 of the Detroit Pistons gets set to take a free throw during the first half of an NBA game against the Toronto Raptors at Air Canada Centre on October 26, 2016 in Toronto, Canada. NOTE TO USER: User expressly acknowledges and agrees that, by downloading and or using this photograph, User is consenting to the terms and conditions of the Getty Images License Agreement. (Photo by Vaughn Ridley/Getty Images)

Australian Aron Baynes has joined the Boston Celtics.

Baynes, 30, has signed a one-year deal, reportedly worth $US4.3 million. He is Boston's third pick up already this off-season, after the adding Gordon Hayward and Jayson Tatum to its roster.

The Aussie big man joins the Celtics after two years at Detroit. He averaged 4.9 points and 4.4 rebounds last season at an average of 15.5 minutes court time.

The Celtics will be Baynes' third NBA franchise, after Detriot and the San Antonio Spurs, where he won the NBA Championship alongside fellow Aussie, Patty Mills.