The move doesn't come as a major surprise. Williams had a non-guaranteed $947,907 contract for 2013-14, but the first $200,000 was set to become guaranteed after Sunday.
With an abundance of players heading to Boston once the blockbuster trade with the Brooklyn Nets is completed, the Celtics freed up a roster spot by cutting ties with the 6-foot-6 Williams.
Williams, 26, appeared in 24 regular-season games for Boston this past season, averaging 4.6 points, 1.8 rebounds and 1.6 assists. He was arrested in May for allegedly brandishing a gun during a visitation exchange with the mother of his child in Kent, Wash., though charges have yet to be filed in the case.