Johnson, 38, last played in the NBA during the 2017-18 season. He was named the MVP of the Big3 this past season and led his team, the Triplets, to the league championship.
He has averaged 16 points per game in 17 seasons in the NBA and was named an All-Star seven times.
The Pistons and Johnson reached a deal last month. He had come to Pistons camp with a non-guaranteed contract. Detroit decided to use roster spots for Christian Wood and continued development of young guard Khyri Thomas instead.