Callaspo's contract, subject to a physical exam, would pay him $3 million next season with an additional $1 million in performance incentives, according to multiple media reports.
"This is not [a deal] that everyone is going to get excited about," Braves president of baseball operations John Hart told MLB.com on Tuesday night. "But these are the kinds of players that help you win. They do little things for you."
The 31-year-old Callaspo played second base, first base and third base this year for Oakland. He hit .223, well below his .267 career average. A year earlier, he batted .258 with 10 homers for the Athletics and Los Angeles Angels.
"When we had our conversations with our scouts before [November's] General Managers Meetings, he was a guy everybody said, 'If he was in shape, we really like this guy,'" Hart told MLB.com. "Well, he had already addressed it. I think with this player there are some bounce-back possibilities.
"He can fill a variety of roles. It's a good fit for us. He's a switch-hitter and a contact bat."
Atlanta traded second baseman Tommy La Stella to the Cubs for right-handed reliever Luis Vizcaino last month. Callaspo and Phil Gosselin could compete for the starting job at second base with top prospect Jose Peraza.
Callaspo also could play behind Chris Johnson at third base.
Callaspo's best season at the plate came in 2009, when he hit .300 with 11 homers and 73 RBIs for Kansas City.
The Associated Press contributed to this report.