Facchinetti said she aims to present her first Valentino collection in March.
"I am honored to be part of this new project," she said, calling Valentino an "icon of style and elegance."
Valentino Garavani, 75, said Tuesday he was stepping down as head designer of the fashion house after 45 years in the business. Over the course of his career, his trademark red gowns have graced the world's royals, Hollywood stars and international jet setters.
Valentino said he would show his last ready-to-wear collection in Paris in October and his couture collection there in January.
Facchinetti began her fashion career at Prada's second line Miu Miu, where she stayed for seven years, eventually rising to become design brand coordinator for both the men's and women's collections.
In 2000, she became design director next to Ford at Gucci; four years later she was named creative director for womenswear when Ford resigned. But Facchinetti resigned a year later in a disagreement with management, and in 2006 joined Italian sportswear maker Moncler