The christening of Archie Harrison Mountbatten-Windsor will be a small, private event with fewer than 25 friends and family members in attendance, the source said.
It will be held at a private chapel in Windsor Castle. Buckingham Palace is expected to release photographs after the event. The ceremony is due to take place exactly two months after Archie was born on May 6.
Harry was christened at St. George's Chapel in Windsor Castle in 1984, and he and Meghan wed there in May 2018.
The chapel was where Prince Andrew's daughter Princess Eugenie wed Jack Brooksbank in October 2018, and where Lady Gabriella Windsor married financier Thomas Kingston in May 2019.
The Sunday Times reported earlier this month that Archie will wear a replica of the historic royal christening gown, which was commissioned by Queen Victoria and first used in 1841 for the baptism of her eldest daughter, Princess Victoria.
The original was made from Spitalfields silk and Honiton lace. It was worn by 62 royal babies, including Queen Elizabeth at her christening in 1926, Prince Harry and Prince William.