The granddaughter of Queen Elizabeth, 28, arrived at her ceremony wearing a off the shoulder ivory dress designed by Peter Pilotto.
Princess Eugenie’s dress features a neckline that folds around the shoulders to a low back that drapes into a flowing full length train, Buckingham Palace said.
The low back feature was specifically requested by Princess Eugenie, who had surgery aged 12 to correct scoliosis, a spokesman added.
Eugenie will now celebrate her nuptials with Jack, 32, in a ceremony conducted by Dean of Windsor David Conner.
Italian opera singer Andrea Bocelli will perform two pieces during the service, with members of the Royal Philharmonic Orchestra also featuring.
Present at the chapel are 850 guests including celebrities such as Victoria and David Beckham, George and Amal Clooney, Sir Elton John, Ed Sheeran, Robbie Williams, Ellie Goulding, James Blunt and more.
Royal family members present include Prince Harry and Meghan Markle, Princess Beatrice, Queen Elizabeth, Prince Charles and Prince Philip amongst others.
7 News is airing every moment of Princess Eugenie's wedding live, as the only Australian broadcaster with cameras inside the Chapel. More info here!
Princess Eugenie’s wedding bouquet is made up of Lily of the Valley, Stephanotis pips, hints of baby blue thistles, white spray roses and trailing ivy.
It was created by Patrice Van Helden Oakes, the sister of floral designer Rob Van Helden.
The floral arrangement also contains sprigs of myrtle from Osborne House, as part of a regal tradition which can be traced back to Queen Victoria.