Mirren donned a dark buttoned-down coat with grey checkered trousers and a cane that the actress used to playfully spin and point at attendees with.
Fonda rocked a form-fitting tiger print dress along with a diamond choker.
Both Mirren, 72, and Fonda, 79, joined L'Oreal as spokeswomen in 2014.
"I have always loved the L'Oreal Paris brand, and I hope I can inspire other women towards greater confidence by making the most of their natural good looks. We are all worth it!" Mirren said at the time.