Emerson, 22, initially joined Barcelona from Brazilian side Atletico Mineiro in January 2019 in a three-way deal also involving Betis, which saw the full-back join the Andalusian club on loan.
Barca have now exercised their option to bring Emerson back to the Nou Camp.
The club have already agreed deals to sign Manchester City duo Sergio Aguero and Eric Garcia this week.
Argentina striker Aguero and Spain centre-back Garcia will join Ronald Koeman’s side on a free transfer when their City contracts expire at the end of this month.
Liverpool midfielder Georginio Wijnaldum has also been strongly linked with a free transfer move to the Catalan club.
Emerson made 79 appearances in all competitions for Betis, scoring five goals and providing 10 assists. He played more minutes than any other Betis player last season as Manuel Pellegrini’s side finished sixth in La Liga to qualify for the Europa League.
He has represented Brazil at Under-20 and Under-23 level before winning his first senior cap in November 2019.