Fergie, 58, wore a green dress paired with a matching hat and heels.
Fergie's other daughter, Princess Beatrice, is serving as maid of honour for the big day.
Other royal family members in attendance include Queen Elizabeth, Prince Philip, Prince Charles, Kate Middleton and Prince William amongst others.
Also 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.
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!