Mack is coming off his best season as a pro for the Hawks, starting 11 of 72 games and averaging a career-best 7.5 points and 3.7 assists per game.
The deal includes a team option in the third year, a source said.
The Hawks are still working to bring back their other restricted free agent, forward Mike Scott.
Mack, 24, has had stops with the Washington Wizards, Philadelphia 76ers and Hawks in his three pro seasons. He was the 34th overall pick in the 2011 NBA draft out of Butler.
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