An England Under-19 international, the youngster made 28 appearances for the Oakwell outfit but now can't wait to get to grips with life at Goodison Park.
"It's been a long day but an exciting day for me and my family," he said in his exclusive first interview with evertontv. "It doesn't feel real and it hasn't sunk in yet but I feel very happy and very proud.
"There are a few nerves because it's a new challenge for me. Every player wants to play in the Premier League and I've left an amazing club which is very close to my heart and left some very good people back there who I can't thank enough. But I've joined an amazing club, I'm here at Everton now and I'm looking forward to every minute of it."
Having joined Barnsley aged just six, Stones made his first-team debut in March last year and quickly established himself as one of the brightest young talents outside the top flight.
"I'm a hard working player and I'll give everything for the team, which every other player here does," he said. "I like to get forward a lot but I'm a defender and that's my job, defending."