The 25-year-old moves to Goodison after failing to break into the Barca first-team picture last term, becoming the Toffees' third signing in the final hour of the transfer window following the arrivals of Bernard and teammate Yerry Mina.
The Portuguese was monitored by a number of top sides over the summer window, including Arsenal and Chelsea, but came onto Everton's radar during their discussions over the £28.5m deal for Mina.
In a statement on their website this evening, Barcelona said: "FC Barcelona and Everton FC have reached an agreement over the loan of the player Andre Gomes for the 2018-19 season
"The English club will pay FC Barcelona €2.25m for the season long loan and will also pay the player's wages."
Gomes made just six La Liga starts under Ernesto Valverde last season.