Although Maguire departed the Dons when his contracted expired, the Scottish club were entitled to a fee.
Now that has been sorted, the Rams are delighted to welcome the 22-year old striker to Pride Park on a three-year deal.
"Chris is an exciting talent who has great potential to improve further," manager Nigel Clough told the club's official website.
"He is a creative player and someone who can bring a spark to the team.
"He's still young and will develop and improve, but having played in the Scottish Premier League and made his international debut he already has the quality to be competitive in our squad and team."