Arriving at the Palladium Theatre in London, Kate wore a black lace Alexander McQueen evening gown with her long hair loose. The dress had a daring scooped back and a sweetheart neckline.
The duchess was presented with a posy of flowers picked from the garden of the Royal Variety Charity’s residential home in west London, Brinsworth House.
This year it is called 'Frosty Winter Garden' and was handed to Kate by Lydia Jones, 10.
Meanwhile a programme was presented to William by Oliver Hinton, eight.
The couple then greeted executive from the Royal Variety charity and ITV who will broadcast the show in early December.
They also got to meet some of the cast of the new well-received Mary Poppins musical, Petula Clark CBE, Zizi Strallen and Charlie Stemp - who play the Bird Lady, Mary Poppins and Bert.
William asked where they were performing and Zizi told him it was the Prince Edward Theatre, opening this week.
"We are doing a show tonight," she added, explaining how the cast were racing to their performance after opening the variety show. "I love Mary Poppins!" William exclaimed.
Petula Clark told Kate she would have to bring the children to the show. "They would love it," she smiled.
The Royal Variety Performance takes place every year, either in London or in a theatre around the United Kingdom.
The event is in aid of the Royal Variety Charity, formally, The Entertainment Artistes’ Benevolent Fund, of which The Queen is Patron.
The money raised from the show helps hundreds of entertainers throughout the UK, who need help and assistance as a result of old age, ill-health, or hard times.
The evening was being hosted by Rob Beckett and Romesh Ranganathan and included performances from the cast of Mary Poppins, Lewis Capaldi, Mabel, Robbie Williams, the cast of Come From Away, and a special collaboration by Emeli Sandé and Manchester’s Bee Vocal choir.
Beckett and Ranganathan jokingly introduced the royal couple, teasing the couple that they were on a "date night" as the camera focused on them laughing and giggling in the Royal Box, William nodding with mock seriousness.
The comedians asked whether they had paid the babysitter to stay "until 12 or 1", joking: "It’s always worth £20 for the extra hour."
Ranganathan said he, like the Cambridges, had three children and guessed that William and Kate thought the same thing when they saw their three little faces running into their bedroom each morning "why did we do this?" The royal couple roared.
There were also a couple of ‘close to the knuckle’ jokes with Beckett and Ranganathan teasingly pointing out their mothers in the audience "sitting on the subs bench like the cast of Loose Women".
Ranganathan even joked that his mother was "technically an illegal immigrant".
Headline act Sir Rod Stewart was unfortunately forced to pull out at the last minute on "strict doctor’s orders" due to a throat infection.
He tweeted that he was ‘absolutely devastated’ to be unable to perform and described it as an ‘amazing show which I love being part of’.
"I’m very disappointed that I can’t be there to give my support," he said.
The origins of the Royal Variety Performance date back to 1912 when King George V and Queen Mary agreed to attend a 'Royal Command Performance' at the Palace Theatre in London, in aid of the Variety Artistes' Benevolent Fund.
In July 1919, the second Royal show was performed and was the first to be billed a "Royal Variety Performance". Held at London's Coliseum, the show was staged as a 'celebration of peace' and, as the official announcement expressed it, "had been commanded by The King to show his appreciation of the generous manner in which artistes of the variety stage had helped the numerous funds connected with the War".
Tonight William and Kate will meet a number of performers as well as Royal Variety Charity and ITV executives, both before and after the show.
The couple have previously attended twice, in 2017 and 2014.