The Braves signed Lamb to a one-year, $1 million deal, according to MLB Media. The agreement was reported Sunday, but the contract didn't become official until the club received the COVID-19 intake testing results Tuesday afternoon.
Lamb, who was an All-Star selection with the D-Backs in the 2017 season, was with the Braves for their first full-squad workout of the spring and will compete for a bench spot.
Braves manager Brian Snitker emphasized that the powerful Lamb was signed for his left-handed bat as a pinch-hitter.
"I think that is why we signed him, the damage he has done," Snitker said Tuesday. "He's had success. Hopefully we get him in here, and he has an opportunity to have another big year.
"... You get late in a game and you need a double-switch, he can be a very valuable asset much like Matt Joyce did a couple years ago. He can be a left-handed bullet on the bench."
Lamb struggled in the pandemic-shortened 2020 season, hitting a combined .193 in 31 games with the Oakland Athletics and Diamondbacks. He finished the season strong, however, batting .267 with three home runs in 13 games after signing with the A's.
The 30-year-old Lamb recorded a .239 batting average with 84 home runs and 312 RBIs in 609 career games with the D-Backs and A's.
The Braves designated left-handed pitcher Phil Pfeifer for assignment to clear a spot for Lamb on the team's 40-man roster.