Kate shimmered in a green dress by Missoni featuring sheer sleves, which she paired with nude heels (a staple in her wardrobe) and a gold necklace.
The dress currently retails for US $2,480.
The party at Empire Music Hall in Belfast was held to recognise young people making a difference in Northern Ireland.
Earlier in the day Kate and William joined a soccer kick-about with school kids.
The royal couple are spending two days in the area.