The LaLiga giants have reached an agreement to secure first option on the midfielder, who would cost €30 million plus €9 million in variable amounts.
FC Barcelona issued an official statement after midday on Sunday to announce that they have reached an agreement with Grêmio de Porto Alegre to reserve an option to buy Brazilian midfielder Arthur Henrique Ramos de Oliveira Melo.
Barcelona have tracked the midfielder since he shone in Gremio's Copa Libertadores triumph previous year.
Barcelona have targeted a deal for the last few months and technical director Robert Fernandez has made numerous visits to Brazil in a bid to thrash out a deal with club and player.
Arthur will join fellow Brazilians Philippe Coutinho, Paulinho, Rafinha, Douglas and Marlon Santos on Barca's books should the move come to fruition.
At Gremio, Arthur broke through to the first team under manager Luiz Felipe Scolari and has been instrumental to the side since.
Arthur has always been linked with both Chelsea and Barcelona, with both sides preparing to meet in the second leg of the Champions League clash next week.