The left back impressed for the Toffees while covering for Leighton Baines last season and will join up with Tony Pulis's side for the 2016-17 campaign.
West Brom has signed defender Brendan Galloway on loan from Everton for the 2016-17 season.
Primarily a left back but also able to play at center back, the 20-year-old joined Everton from MK Dons in August 2014 and made his Premier League debut in May 2015.
He managed 14 starts last term under Roberto Martinez, whose replacement Ronald Koeman has allowed the Zimbabwe-born player to seek more regular first-team action at The Hawthorns.