Harrison will head up atelier's marketing and new business efforts as part of the management team. She will be responsible for the overall operations of the company, reporting into atelier general manager, Janet Carpenter.
At Euro RSCG, Harrison led the business for Yakult, News Group Newspapers (The Sun) and Evian.
Harrison started her career with Lowe Howard Spink in 1996, which was followed by a seven year stint at Publicis, working on Coca-Cola, United Biscuits, Hayward Gallery and The Post Office.
She also helped to set up Publicis Focus, the specialist luxury division where she had direct responsibility for Lancome beauty and fragrances as well as New Business for the agency.
In 2004 she joined JWT where she was board account director for the agency's Kraft and Weight Watchers business, before joining Euro RSCG London in 2006.
Carpenter said: "Antonia has the perfect combination of passion for and experience in beauty, fashion and the luxury sector. She is a great addition to the atelier management team and we are delighted Antonia has joined us."
Harrison said "The atelier role had many magnetic qualities for me – the uniqueness of the atelier offering, the talent already employed here, the business ambition and the fact that the luxury goods sector is booming within the UK and abroad."