The official Twitter handle of Kensington Palace shared a short video of Kate and William arriving at the BAFTAs and wrote: "The Duke and Duchess of Cambridge have arrived."
Kate and William, seated in the front row, smiled for the cameras.
Earlier, they walked the red carpet, accompanied by Amanda Berry, the CEO of the British Academy of Film and Television Arts.
Prince William presented the Fellowship Award to celebrated director Mel Brooks, who is known for comic films like Spaceballs, High Anxiety, Silent Movie and Young Frankenstein.
Prince William and Kate Middleton rarely appear at high-profile showbiz events, although their visit to India last year did include a gala attended by film stars like Shah Rukh Khan. In 2012, they were spotted on the red carpet at the London premiere of director Steven Spielberg's film War Horse.
The BAFTAs top honours were won by the musical La La Land, which scored six awards including Best Film, Best Director for Damien Chazelle and Best Actress for Emma Stone. Viola Davis of Fences was named Best Supporting Actress while Slumdog Millionaire star Dev Patel received the Best Supporting Actor. La La Land star Ryan Gosling lost Best Actor to Casey Affleck for Manchester By The Sea.
The award season is heading to its grand finale with the Oscars at the end of this month. La La Land, which also won seven Golden Globes, is the clear favourite to win top prizes.