The American model joins contestant mentor Eva Lorenzotti and judges Kenneth Cole and Ariel Foxman on the forthcoming series.
The show features 12 designers competing to design the most creative accessories, including jewellery, belts, bags and shoes. For the moment, the names of the contestants remain a secret, but production started in New York last month.
Sims recently became engaged to Battleship producer Scott Stuber. She has claimed that she plans to have the "wedding of the century".
The model was previously praised for her appearance as a guest judge on Project Runway in 2010.
Project Accessory is expected to follow the format of Project Runway, and will premiere later this year on Lifetime.