Barcelona confirmed on Tuesday the signing of Malcom from Bordeaux for 41 million euros plus 1m in add-ons.
He agreed a five-year deal to move to the Camp Nou, with a release clause expected to be fixed at €400m.
Roma had announced on Monday they had reached a deal with Bordeaux subject to a medical and personal terms being agreed but Barcelona hijacked the move at the 11th hour.
Roma supporters had even gathered at the airport in Italy’s capital city to welcome Malcom on Monday night, but he never arrived.
Instead, terms were being negotiated with Barca, who had gazumped Roma’s bid, which was reported to have been in the region of €32m.
— FC Barcelona (@FCBarcelona) July 24, 2018
Malcom, yet to be capped at senior level by Brazil, scored 20 goals and set up another 13 in 84 Ligue 1 games following his 2016 move from Corinthians.
The Brazillian will undergo a medical in Barcelona on Wednesday ahead of his presentation.
He will then join the club for their pre-season tour of the US where he will hopefully make his debut for his new club.