The 17-year-old will produce her own eight-piece fashion range for the company, reports The Mirror.
Pixie is expected to model the outfits at a fashion show in the London flagship store.
"The deal is virtually identical to the one Lily Allen signed," said a source.
"But whereas Lily's was met with a slightly muted response, Pixie's is expected to race out of stores.
"Money can't buy you style but Pixie flaunts hers effortlessly. She's a brilliant role model for young fashionistas."