The 11-week-old, who is fifth in line to the throne, will be baptised by the Archbishop of Canterbury, the Most Rev Justin Welby, in the Chapel Royal at St James's Palace.
Prince George, four, and three-year-old Princess Charlotte will be there for their younger brother's big day.
It will be the first time the Duke and Duchess of Cambridge and their three children have been seen together as a family of five.
Kensington Palace has yet to release the guest list, but royal christenings are usually a small, family affair.
Newlyweds the Duke and Duchess of Sussex are likely to put in an appearance, as are Kate's pregnant sister Pippa Matthews, and her brother James Middleton.
Meghan was christened and confirmed in the Chapel Royal by the Archbishop, who also married the Suits star and Harry at Windsor in May.
Louis' godparents, who will be announced on the day, will take part in the private 40-minute traditional religious ceremony, which begins at 4pm in the intimate, oak-panelled chapel.
There is speculation the Cambridges, who usually opt for close friends and confidantes, may choose William's trusted private secretary Miguel Head, who is leaving the post this month, to be a godfather.
They might even turn to one of William's cousins, Peter Phillips, Princess Beatrice, Princess Eugenie or Lady Louise Mountbatten-Windsor - a move which would delight the Queen.
The baby prince - Louis Arthur Charles - was born in the private Lindo Wing of St Mary's Hospital in Paddington, London, on April 23 - St George's Day - weighing 8lb 7oz.
He will be welcomed into the Christian faith dressed in the same frilly, cream gown used for George and Charlotte.
The robe is a replica of the intricate lace and satin dress made for Queen Victoria's eldest daughter in 1841.
George was also christened in the Chapel Royal, but Charlotte was baptised at the Church of St Mary Magdalene in Sandringham.
After George's christening in 2013, the Prince of Wales and the Duchess of Cornwall gave a private tea at nearby Clarence House, and guests were served slices of christening cake, taken from a tier of William and Kate's wedding cake.
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