The Rams beat off stiff competition for the 26-year-old centre-back, most notably from arch rivals Nottingham Forest, with Barker signing a three-year deal at Pride Park.
"Nigel Clough was a massive factor in my decision to come here," Barker told the Derby Evening Telegraph. "I was born in Nottingham and supported Forest as a youngster. But once you become a professional footballer you stop being a fan and concentrate on doing your best for your club.
"Forest may have shown an interest in me but I am 110% committed to Derby and very impressed by Nigel's plans for the club. He had clearly done his homework on me and as soon as I spoke to him it was clear to me that Derby was where I wanted to be. I can't wait for the season to start."
Clough said: "Shaun has been one of our top targets all summer and we are delighted to have concluded the deal to bring him to Pride Park.
"At 26 years old he is in his prime and has all the attributes we are looking for in a centre half."