Brad is the first male to have fronted a campaign for the couture house’s best-selling fragrance.
He follows in the footsteps of Nicole Kidman, Vanessa Paradis and Audrey Tatou.
Explaining the surprising decision, Fragrance president Andrea d’Avack said: "To keep a legend fresh, you always have to change its point of view."
"We think very much that the perfume is a seduction between a man, a woman and the perfume. No.5 is our leading fragrance, and we are willing to make the investment to keep it on that level."