The royal accessorised the dress with a glittering gold clutch bag designed by Anya Hindmarch, a pair of Jimmy Choo heels and a necklace and earrings from Van Cleef & Arpels.
Eagle-eyed fashion fans will recognise the dress, which the royal first wore in 2012 to attend a dinner with the King and Queen of Malaysia during a tour of Southeast Asia.
By choosing to wear a dress she already owned, Kate was adhering to Baftaâ€™s new sustainable dress code which encouraged guests to either re-wear something they already own or hire an ensemble as opposed to buying something new.
A spokesperson for Bafta said: â€œSustainability is very important to Bafta, and weâ€™re doing more than ever before.
â€œWhere sustainable choices are unable to be made, Bafta is offsetting, as well as giving guests the tools to offset their own travel and make sustainable fashion choices.â€
Ahead of the event, the British award body created a sustainable fashion guide in collaboration with the London College of Fashion, which urged guests use rental fashion sites, source clothing from resale outlets and opt for sustainable fashion brands, such as Stella McCartney, which are renowned for using eco-friendly materials.
â€œThis awards season BAFTA are doing more than ever before to consider sustainability across its awards ceremonies, including inviting guests to â€˜dress sustainablyâ€™,â€ the guide read.
â€œTo help navigate some of the issues around fashion and sustainability London College of Fashion, UAL are supporting BAFTA with more information on how you can dress sustainably.â€
See our roundup of the best dressed guests at the 73rd British Academy Film Awards here.