The Academy Award-winning actress stunned audiences with her breakout role as Patsey in Steve McQueen's 12 Years a Slave.
Nyong'o also recently starred in the action thriller Non-Stop alongside Liam Neeson and Julianne Moore.
She said of the news: "I am truly honoured to join the Maison Lancôme, a brand with such a prestigious history and that I have always loved. I am particularly proud to represent its unique vision for women and the idea that beauty should not be dictated, but should instead be an expression of a woman's freedom to be herself”.
The actress follows in the footsteps of Kate Winslet, Julia Roberts, Penelope Cruz and Lily Collins as ambassadresses for the brand.
She will be seen this summer in campaigns shot by Mert Alas and Marcus Piggott.