The 34-year-old royal donned an ivory, off-the-shoulder Barbara Casasola dress, which was made from a stretchy figure-sculpting material to give off a sporty vibe.
She completed her stunning look with a matching clutch, strappy peach heels and her signature blow-out.
During dinner, Middleton, who normally sports conservative pieces, presented the Art Fund Museum of the Year prize, which is awarded annually to one outstanding museum that has shown "exceptional imagination, innovation and achievement." The honor went to South Kensington's Victoria and Albert Museum of art and design, as confirmed by the official Kensington Palace Twitter account.
Last month, Middleton looked equally fabulous while commemorating the 100th anniversary of the Battle of Somme at the Thiepval Memorial to the Missing. She wore a zigzag-printed Missoni coat over a black dress for the somber occasion, topping it off with pearl earrings and a black pillbox hat.
The World War I vigil was also attended by her husband, Prince William, and his brother, Prince Harry. Hear more in the video below.