In a statement on Thursday, Barca said the cost of the transfer will be 12 million euros and that Emerson has agreed a contract at the Camp Nou until the end of the 2023-24 season.
Betis also confirmed that Emerson will join them on loan until the end of the season, with reports in the Spanish press claiming Betis and Barca will each pay half of the transfer fee.
"FC Barcelona and Atletico Mineiro have reached an agreement for the transfer of Emerson, who will join the Catalan club from July 1, 2019," read a Barcelona statement.
Betis wrote: "Real Betis have reached an agreement with Atletico Mineiro for the transfer of Emerson. The young Brazilian player will play for the club until the end of the season."
Emerson had only spent a year with Atletico Mineiro and is currently in Chile playing for Brazil in the South American Under-20 Championship.
Barcelona said the right-back has been "compared in Brazil with former Barca player Dani Alves".
Emerson is the their fifth signing of the January transfer window after deals were also agreed to bring Jeison Murillo, Jean-Clair Todibo, Frenkie de Jong and Kevin-Prince Boateng to the club.