Jackson, 27, is 6-foot-7 and appeared in one game with the Celtics last season, and another six with the Suns. He has also spent time with the Kings, Mavericks, Thunder and Bucks.
“Ever since [December], me and my agent have kind of stayed in touch with the Celtics,” Jackson said, via Himmelsbach. “Kind of built that relationship. Came out here to join and kind of play a little bit of basketball, so it worked out.”
Jackson performed well for the Celtics in summer league in July, and was almost signed to a standard deal last season.