Barcelona have agreed on a fee with Gremio for the transfer of Arthur, report Globo Esporte, with the Brazilian club set to pocket €30m.
The Blaugrana have been constantly linked to the midfielder since the Tricolor won the Copa Libertadores last year.
The move will occur in January 2019, with the deal expected to be announced this summer.
The 21-year-old is uncapped, but he will hope to squeeze into the World Cup squad for Russia 2018 after receiving his first call-up last October for the qualifiers against Bolivia and Chile.