The Costa Rican star has signed a four-year contract and joins the Toffees for an undisclosed fee.
The 22-year-old has been granted a work permit.
Oviedo told the club’s official website: “I am so very happy. This is a very good opportunity for me.
“The last two or three days have been very stressful and tiring but I am so happy now. I am feeling good and right now everything is positive.
“I know a lot about Everton. I watch Everton games and Premier League games on the TV and it is a very good league.”
