Most of Johnson's veteran-minimum salary is not guaranteed, a source said.
The 6-foot-8, 255-pound Johnson will compete for a roster spot after playing in China last season. He started for the Mavs’ Las Vegas Summer League team this month, averaging 7.8 points and 3.8 rebounds in 20.8 minutes per game.
In two seasons with the Hawks, Johnson averaged 6.5 points and 3.9 rebounds in 15.8 minutes per game.
Johnson is the 16th player on the Mavs’ roster. The team can carry 15 players during the regular season.