It marked a transition for Middleton as she made the first of what are expected to be many public appearances for a variety of good causes.
Middleton, 28, is not officially part of the royal family until her marriage April 29, but this week she joined Queen Elizabeth II and the rest of the family's inner circle at a pre-Christmas lunch at Buckingham Palace, signaling her new status.
She wore an elegant black and white dress cut just above the knee to the charity event, braving high heels despite the slippery conditions as much of England was blanketed with snow. The outfit was topped with a fitted black jacket and a small black handbag.
Middleton and William received some applause as they walked past well-wishers into the Thursford Christmas Spectacular, where he was the guest of honor.
It had been rumored for days that Middleton would attend as well, adding to the excitement surrounding the annual event.
Money raised from the show will be used to help pay for construction of a special cancer unit at a hospital in Cambridge.
During intermission, William and Middleton planned to meet with a group of young cancer patients from the greater Norfolk region.
The choice of a cancer charity for Middleton's first event is seen as a possible indication of the type of charities she may focus on as she develops her royal role.
The couple are to be married at Westminster Abbey on April 29 after a lengthy courtship.
William's brother, Prince Harry, was in Berlin on Saturday to receive a reward for his humanitarian work.