After finishing his senior year at California, Bird was selected with the 56th pick of the 2017 NBA draft by the Boston Celtics. On September 5, 2017, Bird was signed to a two-way contract by the Celtics. Under the terms of the deal, he split time between the Celtics and their G-League affiliate, the Maine Red Claws. Bird made his professional debut on October 20, 2017 against the Philadelphia 76ers. He played 13 minutes and scored 3 points in a 108–98 win over the 76ers.