WATCH: The moment Queen Elizabeth broke protocol by stopping to accept flowers
Eugenie, 29, shared the candid photographs of Wednesday's royal gathering, which Prince Harry, 34, and her sister Princess Beatrice, 30, also attended, to her Instagram.
In one of the photos, the Queen, 93, leads the royals as they step out for the palace bash.
The other two snaps are of Eugenie and Beatrice chatting to guests during the afternoon event.
"This afternoon, my sister and I attended a Garden Party at Buckingham Palace in support of Her Majesty," Eugenie captioned the photos.
"I really enjoyed meeting such a diverse group of people who were all invited in recognition of their work in their respective communities," she said.
The Queen herself caused controversy at the garden party after breaking royal protocol and stopping to accept a bouquet of flowers from a guest at the event.