The 32-year-old rejected the chance to return to Santos for a fourth spell and has instead decided to join the Belo Horizonte club in order to play in the Copa Libertadores.
Atletico Mineiro has signed former Real Madrid and Manchester City attacker Robinho.
The 32-year-old had been linked to a return to Brazil since his short term contract with Chinese club Guangzhou Evergrande expired at the start of February.
Atletico Mineiro had made no secret of its desire to sign the Brazil international as the club looks to enhance its squad for the upcoming Copa Libertadores campaign, though the side had to compete with Robinho's former club Santos, which was keen to lure him back for a fourth spell with the club.