Mills played for the Blazers last season, but during the lockout went to play with the Xinjiang Flying Tigers of the Chinese Basketball Association. He was cut by the Flying Tigers earlier this year because of a hamstring injury, and FIBA cleared him to return to the NBA earlier this month.
Mills was unable to sign with a team until the Blazers renounced his rights on Saturday.
Mills, who played at St. Mary's in California, grabbed international attention when he scored 20 points for Australia in the 2008 Olympics against the gold medal-winning U.S. team.
He was drafted by the Blazers in 2009 and has played 74 NBA games.