The 'Collide' star is the latest name to partner with Talenthouse, who in the last year have worked on creative initiatives with Paul McCartney, Justin Timberlake and Queen among others.
Lewis said of the competition: "I love fashion, creativity and designing my own outfits. I can't wait to see what people come up with.
"I think it's really important to support creative individuals and the future names of tomorrow. I'm passionate about animal welfare and everything I wear always holds true to this - we want to find the next Stella McCartney out there!"
She added: "I'm really happy to be teaming up with Talenthouse to make this special competition work. Good luck everybody."
Lewis will judge the entries alongside Glamour magazine editor Jo Elvin and designer William Tempest, with the winning outfit being brought to life by a professional team.
"I'm extremely thrilled to be joined by Jo and William," Lewis said of the duo's involvement. "They are two people who are leaders in the field of fashion and that I've had the privilege of working with before. They take this competition to a whole new level."
As well as wearing the winning design during a performance, Lewis will model it in a professional photograph for the winner's portfolio. Two runners-up will receive cash prizes and have their designs featured on the singer's official website and social media streams.
The 26-year-old has asked that all designs are animal friendly. Entries must be submitted via the Tourhouse house website by November 17, and the winner will be announced on December 1.
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