The duo arrived - alongside other Royal Family members - at the service with Zara wearing a dress and coat and Mike donning a blue suit for the festive occasion.
It came just hours the final part of Prince Harry and Meghan’s controversial Netflix series - which viciously attacks William - was released.
Mike, who recently took part in reality show I’m a Celebrity, and Zara were joined by other Royals including the King and Queen Consort as well as Price George and Princess Charlotte.
Members of the Royal Family arrived at the festive service
James Manning
The Countess of Wessex, the Duke and Duchess of Gloucester, the Duke of Kent and Princess Alexandra also attended the ceremony.
And Princess Beatrice and her husband Edoardo Mapelli Mozzi, Princess Eugenie and Jack Brooksbank, Price and Princess Michael of Kent, Lady Gabriella Kingston made appearances.
More than 1,800 people gathered in the abbey for the concert, staged to recognise the "selfless efforts of individuals, families and communities across the UK, and celebrate and showcase the joy that human connection and togetherness can bring".
The palace said these principles are "shared and personified by the inspirational guests who have been invited to the abbey in recognition of their tireless work to help and care for those around them".
Prince William paid tribute to his late grandmother Queen Elizabeth II during the festive carol service, just hours after Netflix released Harry and Meghan's fiery finale in which they made several serious accusations against the Royal Family.
The final volume features claims about Meghan’s treatment in the press, her mental health and their relationship with the Prince of Wales.
A passage was read in honour of the late Queen
James Manning
William read a passage from the late Queen's 2012 Christmas message in which she said she was "always struck by the spirit of togetherness" during the festive season and that it was a time "when we remember that God sent his only son 'to serve, not to be served'".
A Christmas tree in the abbey was decorated with small Paddington Bear decorations, a nod to the late Queen's famous sketch, while guests were greeted with atmospheric snowflakes from a snow machine as they arrived at the entrance.
