The Frenchman has penned a three-year deal with Everton, who have the option of adding a fourth season.
Watford will receive £20m (€22m) for Doucoure, one of their best performers in recent years.
— Everton (@Everton) September 8, 2020
In his first interview as an Everton player, Doucoure revealed that he has wanted this move for a long time.
“I have been waiting a long time to come here and now it has happened so I am very happy,” Doucoure said.
“I had some interest from other clubs but from the beginning when Everton showed an interest in me I told my agent to focus on Everton.
“It was the only club I wanted to join.
“Everton has a big history in English football and it is a good club for me to have a step up in my career.
“I am very happy now to be an Everton player and very excited for the future.”