Doria Ragland, Meghan's mom, will be by her daughter's side for the big day, though one person will be absent for the occasion -- Queen Elizabeth, who has a prior commitment. Both the Queen and her husband, Prince Philip, were absent for Prince Louis' christening last year.
According to a source, Prince Charles and Camilla, the Duchess of Cornwall, will attend the ceremony, along with Prince William and Kate Middleton.
While Harry and Meghan are keeping mum on details of the day, another source says, Justin Welby, the Archbishop of Canterbury, who married the couple and has become "close to Meghan after her baptism," will preside over the ceremony next weekend.
The ceremony is expected to take place in a private chapel near St George’s Chapel, where the couple were married and Harry was christened in 1984.
ET has learned that Archie will follow royal tradition by wearing the replica christening gown worn by royal children, which was made by Angela Kelly, Dressmaker to The Queen. The Queen commissioned the replica gown so that the original, which was made in 1841, would be preserved.
Archie will be baptized with holy water from the River Jordan using the silver Lily font -- a silver font, which has been used in royal christenings since 1841.
Performing at the ceremony will be members of St. George’s Chapel Choir, which has sung at royal celebrations including an event in honor of Prince Charles’ marriage to Camilla in 2005.
Following the ceremony, Archie will be taken into the Green Drawing Room for photos.
Last month, a source told ET all about how the Duke and Duchess of Sussex are doing since the birth of their son.
Harry is "sharing the parenting duties with his wife," according to the source. The Duke wants to be as "involved as possible," and, like every parent, is feeling the effects of the sleepless nights, exhausted but enjoying every minute of it, the source added.
Meanwhile, Meghan "is radiant, taking each day one day at a time," the source said.