The actress will also front ads for the Double C de Cartier handbag.
Lily admits she has always been a fan of Cartier, thanks to her mother's love of quality watches.
"My mom always used to wear Cartier men's watches when I was growing up," she tells WWD.com. "I remember loving the oversized look of it on her wrist, and then for my 18th birthday, she gifted me a watch, saying it would be with me my whole life."
"I just have these familial memories associated with the (fashion) house... but I never imaged that I would officially be a part of the family."
The upcoming collection - an extension of the Clash de Cartier collection which launched in 2019 - includes spiked rings, bracelets, and earrings made of white gold, onyx, diamonds and amethyst, as well as two new timepieces.
Paying tribute to the company's latest fashionista, Arnaud Carrez, Cartier's international marketing and communications director, says, "When it came to expressing the duality of the Clash Unlimited jewellery, Lily Collins was the obvious choice. Unique and committed, Lily Collins embodies a new generation of artists who dare to reveal their different sides, sometimes classic and elegant, sometimes creative, sometimes even extravagant. In summary, people who do not limit themselves."
The capsule collection is set to drop next month (Sep21).