Harrison completed a medical with Everton and signed a one-season loan contract with the club on Sunday night.
The winger had a clause in his contract that allowed him to leave Leeds on loan following their relegation from the Premier League last season.
Aston Villa also had a deal in place with Leeds, but the Midlands club had concerns over the player’s injury status.
Everton do not have an option to buy in the loan agreement with Leeds but they are keen to sign him on a permanent deal.
Sean Dyche is a fan of Harrison and Everton are likely to try and sign him on a permanent deal in due course.
The Toffees will have to negotiate a transfer fee with Leeds, which is part of their current plans.
Harrison has been expected to remain out of action until the September international break due to an injury.
