The candid shot was taken by wedding photographer Alex Bramall, in between the official portraits taken following the ceremony at St George's Chapel.
Sharing the photograph, Eugenie posted: "Jack and I would like to thank everyone who was involved in making our day so special and for all the wonderful wishes as we start married life laughing together. @alexbramall"
Eugenie wowed in a stunning wedding gown by Peter Pilotto and Christopher de Vos on her wedding day, before changing into a pale pink evening gown by Zac Posen.
It is the first time that Eugenie has posted on social media since her wedding day, after posting a series of snaps in the run-up.
Her mother, Sarah Ferguson, posted a series of photographs on Twitter and Instagram on Monday - just moments after Prince Harry and Meghan announced they were having a baby.
Some saw the flurry of posts to be a swipe at the couple for telling members of the royal family about their baby news at Eugenie's wedding.
Fergie, 58, shared a series of photographs from the wedding, including one thanking the designer of her dress for the outfit she wore for the evening reception on Friday night.
She then posted three further messages saying how "proud" she was of Eugenie and Jack - but made no mention of Harry and Meghan.
