Juventus midfielder Miralem Pjanic will join Barcelona at the end of the season in a swap deal with Brazil international Arthur.
Bosnian Pjanic, 30, has agreed a deal worth an initial 60m euros (£54.9m), with a further 5m (£4.6m) in add-ons.
He made 214 appearances for Serie A champions Juve after joining in 2016.
Meanwhile, Arthur, 23, who joined Barca from Gremio on a six-year deal in 2018, will move for an initial 72m euros (£66m), with 10m (£9.1m) in add-ons.
Arthur will remain with Barcelona until the end of the season.
Juve are four points clear at the top of Serie A as they chase a ninth consecutive title.