Kate, 32, dazzled in a floor-length, pale blue Jenny Packham dress as the guest of honor at the black-tie event at London's Natural History Museum.
Kate, who is a patron of the museum, joined television naturalist Sir David Attenborough to present the Wildlife Photographer of the Year Awards after meeting finalists and viewing an exhibition of their work.
In front of 400 guests in the Hintze Hall, which is dominated by a giant Diplodocus skeleton, Kate gave out the awards. Coming in first was American photographer Michael "Nick" Nichols, who was named Wildlife Photographer of the Year. His winning entry was a black-and-white image of lions resting with their cubs in Tanzania's Serengeti National Park.
It was the second official outing of the day for keen amateur photographer Kate, who had not been seen in public since she announced her second pregnancy Sept 8.
With her first trimester behind her and her health improving following severe pregnancy sickness, she was clearly relishing being able to be out.
Kate presented awards to the overall winners of the adult and under-18 competitions alongside Attenborough and Sir Michael Dixon, director of the Natural History Museum.
The show celebrates the rich diversity of life on our planet while highlighting the fragility of nature.
Shortly after she arrived, Kate was presented with a posy by Sophie Milner, 13, daughter of Dr. Jonathan Milner, a trustee of the museum.
She also met underwater photographer Alex Mustard, 39, from Peterborough. "How did you find yourself under water?" she asked him. "Well, it's just really because there's so much to shoot," he replied.
Pointing out his photo to her in the exhibition, he told Kate, "It doesn't sound too glamorous, but it's a very colorful picture."
After meeting the finalists, Kate took her seat between Attenborough and Dixon for the main ceremony.