The 18-year-old will join the Bluebirds tomorrow and could make his debut when they visit Eastleigh on Saturday.
Donohue was part of the Toffees under-18 side who won the Premier League title in 2013/14 and has represented both the under-18s and under-21s this season.
He joined the Blues’ Academy aged 10 and signed his first professional deal - a two-year contract - in July 2015.