The midfielder will be presented at the club next Thursday in front of fans at the Bernabeu.
He will then head to the United States to join his new team-mates on their pre-season tour.
Ceballos, 23, made his Betis debut in 2014 and two years ago signed a new contract util 2020.
But after a stellar campaign last term both Real and Barca made moves to trigger his release clause.
Real are understood to have paid a fee higher than that clause as a goodwill gesture to Betis.
Ceballos will cost the Spanish and European champions just under £16million.
He becomes their second acquisition of the summer after Theo Hernandez joined from Atletico Madrid.
Real this week loaned out playmaker James Rodriguez to Bayern Munich and are expected to offload both Danilo and Alvaro Morata before the summer is out.
Source:www.express.co.uk