The singer, who serves as executive producer on new Sky Living series Styled To Rock, wanted to set the show in Britain's capital to tap into its wealth of undiscovered talent.
"London has always been one of my favourite cities to come to. I always go out on the street walking around to see what the kids are doing. They always set the trends for the designers," she told The Sun.
"I find that the kids in London have so much style, so much street style and so much talent. This show was a way for me to give these kids the opportunity to see how far they can go.
"We're hoping to find the next superstar designer to dress superstars. What I'm really looking to find is the next innovative young designer, someone like Vivienne Westwood or Alexander McQueen.
"These designers are actually the fashion kids on the street who don't have the opportunity to get to the next step. The fashion kids always do something new, always do something innovative and that's what this competition is all about, and that's why I came to London.
"I really wanted to do this show because I love discovering new designers and finding things that are fresh and trendsetting."
Rihanna added that it's going to take "a lot of guts", "confidence" and "skill" to be the winning designer.
Cheryl Cole, Katy Perry, Little Mix and Pixie Lott make guest appearances on Styled To Rock, which starts tomorrow at 9pm on Sky Living.
Watch Nicola Roberts and Henry Holland discuss Styled To Rock with Digital Spy below: