Based in London, she will work for the production company full-time and is in discussions about scripts.
Ali left WCRS in January without a job to go to. However, she has spent the past three months working for the agency as a consultant on 3, the account she handled during her year at the agency.
Madeleine Sanderson, the Partizan London managing director, said: "We are very excited about signing Leslie. She is talented, inspiring and passionate about her work."
Ali has just completed a campaign for 3 but it is unlikely that she will be working with WCRS and 3 in future. While she was at WCRS, Ali worked with Leon Jaume, overseeing a creative department of 22. Ali and Simon Robinson, a creative director, were responsible for the "jellyfish" and "cherry" spots for 3. She also worked on BMW.
WCRS hired Ali four months before finalising its management buyout last April. She was the only senior member of the team not to buy a stake in the agency. In the five years before this, the US-born Ali served two stints at DDB, between which she attempted to set up the ad agency Ground Zero Advertising in New York. When this failed, she returned to DDB, where she worked as an art director on the account for the Volkswagen Golf. She was also a creative director on The Guardian's account.
Ali has also worked for Clemenger BBDO in Sydney, Foote Cone & Belding San Francisco and Wieden & Kennedy Portland in the US.