Richardson, 34, did not play for more than two years after a knee injury in January 2013. He returned Feb. 20 and played 19 games for the Philadelphia 76ers, averaging 9.1 points.
Richardson will receive a $1.45 million veterans minimum and will try to make the Hawks roster out of training camp.
He has been in the league 14 seasons and has career averages of 17.1 points and five rebounds per game.
Yahoo! Sports first reported the Hawks' interest.