The highly-rated 18-year-old worked his way through the youth ranks at Oakwell and made his first team debut for the Tykes in a Championship defeat against Reading last season.
And, despite only making 24 appearances for the South Yorkshire outfit, Toffees boss David Moyes has seen some potential in Stones and snapped him up just ahead of Thursday evening's 11pm deadline.
Stones has plenty of pace and can also operate in the centre of defence so his versatility was no doubt a big attraction to Moyes when looking to sign him.
And the player is relishing the opportunity to ply his trade in the Premier League for the Merseysiders:
Stones said: "I am very excited to be joining Everton. I've been very impressed with everything I have seen at Finch Farm already."