The 21-year-old defender arrived at Oakwell yesterday, signing a three-year deal with the Reds and he spoke EXCLUSIVELY to iFollow!
The Southampton academy graduate expressed his delight at putting pen to paper on a permanent deal with the Reds.
He told us: "I'm absolutely delighted! Thrilled to get it over the line. It's the perfect next step for me, and to be signing for a Championship club like Barnsley as well, I've walked around the place and you really get a feel for it, the history of the club.
"It was a really easy decision for me to make. I went and met the manager, and I got really good impressions straight away. I felt comfortable, and knew I'd made the right move right away."
After two successful loan spells with Wycombe Wanderers and Walsall respectively, McCarthy feels it's the ideal time to step up and believes his game will fit with the brand of football that Paul Heckingbottom's side are renowned for.
"I like to get the ball down" he explained. "To get it down and play through the lines. I love to get forward from right back. That's another key reason that drew me to the Club, the way Barnsley like to play, I think it will suit me well.
"The Gaffer sees me as a right back and I like that, because I had a really good season playing there with Walsall and really enjoy my football in that position."
Watch the full FIRST INTERVIEW with Jason McCarthy over on iFollow now!