Following the service, where Prince Louis was flanked by six godparents, the royals made their way to Clarence House where they enjoyed an intimate afternoon tea with guests.
The chapel holds tremendous significance for the royal family: Louis' elder brother Prince George was also christened there, and the chapel was where the late Princess Diana's body was laid before her funeral.
Louis' godparents are a mix of close friends and family members: Nicholas van Cutsem, Guy Pelly, Harry Aubrey-Fletcher, The Lady Laura Meade and Robert Carter are all friends of the Duke and Duchess' and and Lucy Middleton is Kate's cousin.
Dominic Lipinski/Pool via REUTERS Britain's Catherine, Duchess of Cambridge, carries Prince Louis as they arrive for his christening service at the Chapel Royal, St James's Palace in London, on Monday.
According to the post, the Duchess of Cambridge was christened on June 20, 1982, which just so happens to be the day before Prince William was born.
Queen Elizabeth, 92, has also begun to scale back her duties because of her advancing age, handing over some of her responsibilities to her heir, Prince Charles.
Then the couple will have a whole day of activities in Dublin on Wednesday, including a trip to Trinity College, to see the Book of Kells, considered one of Ireland's greatest cultural treasures.
The queen, dressed in a royal blue outfit with turquoise edging, later hosted a ceremony to present the RAF with a new Queen's Colour, at which she recognised the service's work.
Prince George and his younger sister, Princess Charlotte, were snapped at Buckingham Palace watching a Royal Air Force flypast from a window.