The 48-year-old World War Z star will reportedly make history as the famous fragrance's first male model.
Pitt will shoot his first campaign for the brand in London this week, according to E! Online.
He will reportedly receive a seven-figure sum for the advertisement, which is tipped to debut towards the end of this year.
Pitt follows in the footsteps of previous Chanel No.5 brand ambassadors including Catherine Deneuve, Nicole Kidman, Lauren Hutton, Audrey Tatou, Estella Warren and Ali MacGraw.
The star and fiancée Angelina Jolie were recently reported to have purchased a new home in London.
The Hollywood pair decided to buy the property - named Whornes Place - while renting it for £30,000 ($48,000) a month last summer. Pitt was filming zombie thriller World War Z last summer when they were staying in the capital city's borough of Richmond with their six children.
Watch Brad Pitt in a clip from sports movie Moneyball below: