The singer recorded a commercial for the credit card company in New York this week, and will be promoting the American Express Gold and Platinum cards.
Knowles will be following in the footsteps of other stars such as Kate Winslet, Robert DeNiro, Ellen Degeneres and Tiger Woods, who have all been spokespeople for American Express.
A source told the American magazine OK!: "Beyoncé is a role model for so many young people. She has tremendous cross-over appeal the same way Tiger does. She’s an inspiration for lots of people. She’s a great fit for American Express."