The 21-year-old, who made one senior appearance for Saints against Crystal Palace in December 2014 and also captained the under-21s to the Premier League Cup success in 2015, has signed a three-year deal at Oakwell.



McCarthy spent the 2016/17 campaign on loan at League One Walsall, playing every minute of league and cup action and scoring five goals on his way to being named as their Player of the Season.



Prior to that, he made 39 appearances in all competitions for Wycombe Wanderers on loan and was also named as the club’s Player of the Season.



Southampton Football Club would like to Jason for his hard work and wish him every success for the future.