The princess thanked those who took part in the service, including Hugh Bonneville, the actor who starred in Padington, and Melanie C, the singer.
She also spoke to Princesses Eugenie and Beatrice before coming back out to welcome her husband and two children.
More than 1,800 people gather at the abbey for the concert, held to recognize the “selfless efforts of individuals, families and communities across the UK and celebrate and showcase the joy that human connection and togetherness can bring”.
Kensington Palace said the second carol service the princess has held is dedicated to the late queen and the values she displayed throughout her life, including “duty, empathy, faith, service, kindness, compassion and support for others” .