Louis' godparents will be announced on the day, but judging by George and Charlotte's christenings, they are likely to be close friends and confidantes of William and Kate.
Grandfather Prince Charles and his wife the Duchess of Cornwall were also in attendance, along with Louis' maternal grandparents Carole and Michael Middleton and Kate's pregnant sister Pippa with husband James Matthews.
Catherine's parents and siblings will be at the service.
Mrs Carter is a schoolfriend of the Duchess, while Miss Middleton, a solicitor, is her cousin.
Prince Harry didn't spare any expense when it came to his nephew's gift ahead of Prince Louis' christening in the Chapel Royal at St James's Palace.
The Queen did attend both Prince George and Princess Charlotte's christenings in 2013 and 2015.
Another well-known name to appear on the list of godparents includes Guy Pelly, who is the owner of the London nightclub Tonteria. In April he underwent planned hip surgery, but attended the wedding of Prince Harry and Meghan Markle just a few weeks later, walking unaided.
Prince Louis will be christened behind closed doors in a private ceremony.
The Palace also confirmed that Kate Middleton and Prince William's youngest child will wear the handmade replica of the Royal Christening Robe, made by Angela Kelly, Dressmaker to The Queen. Pelly is the son of Princess Diana's close friend Lady Caroly Herbert. For Princess Charlotte's big moment in 2016, Middleton dressed in head to toe white in an Alexander McQueen dress (which she wore again in 2017), with delicate silver jewelry and a flower-filled fascinator.
A royal source said it had been agreed some time ago that the 92-year-old queen would not attend the small, family affair and her absence was not due to any health issues.
The Lily Font is another piece of royal history present at Louis's christening.