Infante's signing was first reported by MLB Network's Jon Heyman. Atlanta has not confirmed the deal.
Infante, 34, spent two-plus years with the Royals and helped them reach the World Series in 2014. He had a career-high 66 RBIs in the regular season, and had a .924 OPS in the World Series.
"He was a tremendous contributor for us in 2014," Royals general manager Dayton Moore said earlier this month. "And he contributed to our team last season."
But Infante struggled with injuries last season, and hit .239 this season in 39 games. He also failed to make several key defensive plays and the Royals designated him for assignment earlier this month. After Infante cleared waivers, the Royals released him.
The Royals, who signed Infante to a four-year, $30.25 million deal after the 2013 season, still owe Infante slightly more than $14 million on his deal.