The Prince, just 11 weeks old, was "very relaxed and peaceful", his mother said, as she told the Archbishop of Canterbury, the Most Rev Justin Welby: "I hope he stays like this".
The Duke and Duchess of Cambridge with Prince Louis outside the Lindo Wing at St Mary's Hospital in Paddington, London.
Kate also remained loyal to her classic look, wearing an elegant McQueen dress once again for the occasion.
In addition to the cake, Prince Louis's christening gown was also recycled.
The decision of the Queen and the Duke of Edinburgh not to attend the service at the Chapel Royal, St James's Palace, was revealed a few hours before the ceremony.
Lady Laura Meade is married to Prince William's close friend James, who is Princess Charlotte's godfather.
What did Prince George wear?
While they have not been named, William's private secretary Miguel Head - who leaves the post this month - is the bookies' favourite to be among the godparents. All yes were of course on little Louis, but also on Charlotte's gorgeous little outfit which consisted of a baby blue dress, matching shoes and the cutest bow hairband by Pepa & Co.