"Barcelona and Arsenal have reached a deal for the Brazilian striker Gabriel Jesus," said the Catalan club in a statement, with Spanish media reporting that they paid the Gunners around 10 million euros (£8.5m).
Jesus arrives to bolster an attack weakened by the departures of Robert Lewandowski and Ferran Torres earlier this summer.
Spanish champions Barcelona pursued Alvarez through the summer but Atletico refused to negotiate with the Catalan giants.
Jesus joined Arsenal in 2022 after a successful stint with Manchester City, where he won the Premier League title four times.
The Brazilian added a fifth league title to his trophy cabinet last season with the Gunners, but was kept out of the team after suffering an ACL injury at the beginning of 2025.
Jesus departs Arsenal having made 123 appearances, scoring 32 goals.