The 20-year-old has signed a pre-contract with the Catalan outfit and will join the club next season.
Emerson becomes Barca's third signing for next campaign after securing the services of Jean-Clair Todibo and Frenkie de Jong.
Barca's statement read, "FC Barcelona and Atlético Mineiro have reached an agreement for the transfer of Emerson Aparecida Leite de Souza Junior. The Brazilian will be officially joining the Catalan club on 1 July 2019.
"The fee has been set at €12m and the player will be signing for the next five seasons, through to 2023/24.