The actress saw off competition from runner-up Corbin Bleu and third placed Jack Osbourne to take home the mirrorball trophy with professional partner Derek Hough, who nabbed a historic fifth win.
During the two-hour finale, Riley wowed the judges one last time with her Samba-Quickstep fusion dance, which garnered a perfect score of 30.
Riley was left stunned at the result, saying, "I did this competition because I didn't know if I could do it. And anything that scares me, I wanna do. I want to let women of all sizes know - you can do whatever you put your mind to. It doesn't matter what size you are, what colour you are, you can do whatever whatever whatever you put your mind to."
The finale of the 17th season also featured musical performances by Enrique Iglesias, Lady Antebellum, Colbie Calliat, and What Does the Fox Say? hitmakers Ylvis.