As part of the event, a roaring aircraft formation passed over Buckingham Palace at 1pm made up of various RAF aircraft, said to be one of the most impressive displays since the coronation of the Queen in 1953.
The 3-year-old looked angelic as she walked in holding hands with her dad, Prince William, and carrying what appeared to be a program for the church service. His great-grandmother Queen Elizabeth and the Duke of Edinburgh did not show up.
The final guests were the young prince's six godparents and their spouses, all of whom are friends or family of the Duke and Duchess.
The Duke and Duchess of Cambridge chose hymns O Jesus, I Have Promised and Lord of All Hopefulness for the ceremony. The christening cake served at the tea is a tier taken from William and Kate's eight-tier wedding cake.
Prince Louis is fifth in line to the throne. They were joined by Prince Charles and the Duchess of Cornwall.More news: Tory chaos: divisions over Brexit continue in wake of resignations
Hours ahead of Prince Louis' christening on July 9, Kensington Palace revealed the names of the baby boy's godparents. James too wore a blue suit and light blue tie while Pippa co-ordinated in a light blue pleated Alessandra Rich dress with silver pumps and a headpiece.
Guy Pelly: The son of wealthy Kent landowners, Mr Pelly used to help run several London nightclubs.
Princes William and Harry's tragic childhoods are well known: The brothers were just 15 (William) and 12 (Harry) when their mother was killed in a auto crash in Paris.
Next is Hannah Carter, an old friend of Kate Middleton's from Marlborough College who is married to Robert Carter. It's an interesting choice for the mother-to-be, who in the recent weeks has flaunted her growing bump in chic maternity wear.
And finally, Middleton, is, as you'd expect, is a cousin of Kate's.
Aubrey-Fletcher is yet another longtime friend of William's, according to People.