Tuesday's transaction comes after Williams, 27, led France to a silver medal at the Paris Olympics.
Williams averaged 7.7 points, 4.7 rebounds, 3.2 assists and 1.5 steals in 46 games (44 starts) for the Storm from 2022-23.
Williams is expected to join the team next week in Seattle.
She owns career averages of 7.1 points, 3.9 rebounds and 2.3 assists in 135 games (80 starts) with the Chicago Sky (2018-20) and Storm.
Williams averaged 15.5 points and 4.8 assists in Paris, including a team-high 19 points in France's 67-66 loss to the United States in the gold medal game.
--Reuters--