The 6-foot-1 Williams was the pivotal player, with Cavaliers guard Damon Jones going to Milwaukee along with Oklahoma City point guard Luke Ridnour and swingman Adrian Griffin. Oklahoma City got Cleveland forward Joe Smith and Bucks forward Desmond Mason.
Last season, Williams, a former second-round pick by the Utah Jazz, averaged 17.2 points, 6.3 assists and 3.5 rebounds per game.
He is expected to ease the offensive burden of star swingman LeBron James.
Williams has five years and $43 million left on a contract he signed last summer with Milwaukee.
Jones, a 10-year veteran, averaged 6.5 points and 1.9 assists per game. Smith averaged 10.1 points and 5.2 rebounds per game and was a part of a trade with Chicago that sent Ben Wallace and Wally Szczerbiak to Cleveland last season.