The Prince of Wales and Duchess of Cornwall - William's father and stepmother - attended the ceremony, as did Catherine's parents, siblings and brother-in-law, according to Kensington Palace.
Prince Harry spent £8,000 on a first edition of Winnie-The-Pooh as a christening present for his nephew Prince Louis.
Meghan and her husband looked relaxed and happy as they entered the venue side by side, along with other members of the royal family.
The christening itself is quite the family tradition, Royal Central U.K. notes, adding Prince Louis also wore a replica of the now-famous Honiton lace christening gown.
The Duke and Duchess of Cambridge has an emotional attachment with the anthem titled "This is the day which the Lord hath made" as it was composed in 2011 for their royal wedding.
Meghan opted for an olive ensemble for Monday's christening of nephew Prince Louis, her first royal baptism since marrying Prince Harry.
His elder brother George was also christened in the Chapel Royal, but sister Charlotte was baptised at the Church of St Mary Magdalene in Sandringham.
The family the made the short trip back to Buckingham Palace for a military ceremony followed by a flypast, which the royals viewed from the balcony of the palace.
Thankfully for the Duke and Duchess of Cambridge, Louis was very well behaved during his eagerly anticipated christening, and the 11-week-old stayed fast asleep as his mum carried him into the chapel.
Another well-known name to appear on the list of godparents includes Guy Pelly, who is the owner of the London nightclub Tonteria. He has been banned from driving three times, including twice for drink-driving and once for speeding. Picture: AAPNicholas van Cutsem is another godparent. His daughter, Florence, was a bridesmaid at the Duke and Duchess of Sussex's royal wedding in May.
Still intact after eating the seven-year-old cake, Kate was out today attending a service at Westminster Abbey to commemorate 100 years of the RAF.
Lucy Middleton is the Duchess' cousin and the sister of Adam Middleton, another of Princess Charlotte's godfathers.