The midfielder completed his switch to Pride Park from Premier League side West Bromwich Albion earlier today.
Following the confirmation of the switch, 21-year-old Thorne said on Twitter: "Delighted to have finally joined @dcfcofficial. Cant wait to get started. Firstly like to thank @WBAFCofficial for everything. Forever grateful and wish you all the best. Just felt it was right move for my career."
Thorne has signed a four-year contract with Derby.