The 21-year-old has signed a three-year-contract - with the option of a further year - in a deal worth £4.2million.
Deulofeu impressed on loan at Goodison Park in the 2013-14 campaign but returned to his parent club and was subsequently loaned out again to Sevilla.
However, Toffees boss Roberto Martinez, who had a good relationship with Deulofeu, has kept tabs on the youngster and moved quickly to make him his first signing of the summer.
Source : PA
Source: PA