Mary looked stunning in a magenta ensemble, pairing a pencil skirt with embellishments with a chiffon, key-holed blouse.
The Crown princess paired the look with a matching clutch and pumps.
Prince Frederik oped for a navy suit and electric blue tie to accompany.
The P4G Copenhagen Summit is an event that fathers Head of States and Government, leaders of international organisations, businesses, academia, and the civil society from around the world to form a powerful coalition on the sustainable development goals through innovative partnerships.
The Summit aims to accelerate and showcase partnerships with scalable solutions to some of the world's challenges in food and agriculture, water, energy, cities and circular economy.
Mary and Fred's latest outing comes after the Australian-born princess was forced to attend several events solo as Fred recovered from back surgery.