Wearing a pale pink Alexander McQueen coat and matching hat, Kate, who is eight months pregnant, travelled to the pageant in a carriage with the Duchess of Cornwall and Prince Harry.
She smiled and waved at the crowds lining the route as the carriage drove to the televised military spectacle which is held every year at Horse Guards Parade in London’s Whitehall.
Other senior royals also arrived in carriages before the Queen made her entrance.
Absent from the event was the Duke of Edinburgh, who is still recovering in hospital from exploratory abdominal surgery.
Instead the Queen invited her cousin, the Duke of Kent, to join her in her glass coach for the short journey from Buckingham Palace along The Mall.
Built in 1881 as a town coach for the Lord Mayor of London, it was purchased for King George V’s coronation in 1911.
It has been used for most royal weddings since then, including by the Queen when she married Philip in 1947 when she was still Princess Elizabeth.
Thousands of people, including friends and family of some of the more than 1,000 soldiers taking part, packed into seats and stands around to watch precision marching by hundreds of Guardsmen.
The Queen took the royal salute as members of the royal family looked on.
It is thought to be only the third time that Philip has missed the event after not attending in 1962 and 1968 when he was away on royal tours.
Taking part in the ceremony on horseback are the Prince of Wales - who is Colonel of the Welsh Guards, the Princess Royal - who is Colonel of the Blues and Royals, and the Duke of Cambridge - who is Colonel of the Irish Guards.