Roy finished ahead of Christine Majerus (Boels Dolmans) and Sunweb's Leah Kirchmann at the end of the 133km stage from Chesterfield to Derbyshire.
"I'm really excited, elated and thrilled to take the victory, especially given the efforts that the team have put in for the past few stages,” Roy said.
"Gracie [Elvin] was in the break yesterday and got caught with five kilometres to go, which was both exciting and disappointing, so for us to have another dig today and pull it off was awesome.
"I was preparing for a bunch sprint because the girls behind were lighting up. We just happened to dig really dig on an uncategorised climb towards the finish.
“I took a few fewer turns but [Christine] Majerus really put the hammer down. I just held her wheel and I took over on the descents.”
Katarzyna Niewiadoma (WM3 Energie) held on to the race lead at the conclusion of the stage but only after resisting a stern challenge from her rivals on the roads of Derbyshire.
Leading from Stage 1, Niewiadoma faced her strongest challenge yet, with Majerus at one stage becoming the virtual green jersey on the road and ending the day in second overall at 1min 25sec.
Kirchmann also jumped up the order, elevating herself to third overall, 11 seconds behind Majerus.
"I knew it was a really dangerous move and I knew we had to start riding to bring her back. I tried to stay calm and relaxed and only think positively,” Niewiadoma said.
"As soon as you start thinking negatively you become nervous. What made it easier for my head is that I knew the course was hard and the climbs suit me. I also knew that some teams would be destroyed on this course; it wasn't easy to stay in the front group.”
Kirchmann was part of a day-long three rider break including Shara Gillow (FDJ Nouvelle Aquitaine Futuroscope) and eventual winner Roy that was joined by Majerus, who bridged the gap from a small chasing group with 77km of racing remaining.
Buoyed by Majerus’s presence, and with no chase initially behind, their lead swelled but with Cervelo Bigla and Canyon-SRAM aiding the isolated Niewiadoma in the chase, they were gradually reeled back in, with Roy, Majerus and Kirchmann contesting the finish.
Having saved her legs for the finish, Roy led from the front outsprinting Majerus on the cobbled finish line, with Kirchmann coming home third for the final bonus seconds.