The christening will be a private ceremony for 2-month-old Archie, who was born on May 6.
"It's a much smaller venue, so we're expecting a more intimate gathering of around 25 people," ABC News' royal contributor Victoria Murphy said.
Prince Charles and his wife Duchess Camilla will be in attendance, along with Prince William and Duchess Kate, who just announced a royal trip in the fall to Pakistan. Meghan's mother, Doria Ragland, will also attend. Queen Elizabeth II, however, won't be able to make it due to a prior engagement.
Archie's christening breaks from recent royal tradition in that the public will not be allowed to see the guests as they arrive, as Harry and Meghan are determined to maintain some privacy for their only son.
The couple is expected, however, to release official pictures from the event.
The decision to keep Archie's christening private has been criticized by many throughout Britain, who feel entitled to be part of Archie's big day as taxpayers paid over $3 million for the renovation of their new home, Frogmore Cottage.
"There was some criticism, some debate when the Sussexes said that they wanted to keep their birth plans a bit more private. We're seeing the same thing is happening now with their christening plans," Murphy told ABC News.
The royal couple is also unlikely to announce the names of Archie's godparents, but according to Murphy there won’t be any big names on the list.
“We’re not expecting to see any celebrity names there so no Clooney, no Serena Williams,” she said. "They’ve gone for their close friends without such big profiles."
Royal babies typically have around six godparents and Harry and Meghan are likely to follow that tradition, according to Murphy.
"My understanding is that the couple have chosen their close friends," Murphy said.
The names of whom Harry and Meghan may include as godparents include Jessica Mulroney and Benita Litt, all close friends of Meghan's. On Harry's side, his cousin Princess Eugenie, mentor Mark Dyer and close friend Jake Warren are all names to watch, according to Murphy. Harry could also honor his mom, the late Princess Diana, by choosing one of her close friends or siblings.
Prince William and Kate are not expected to be included as godparents.
"Harry is not godparent to any of their children," Murphy said. "I think this is a recognition of the fact that as an uncle or aunt you already have an important role."
News of Archie's planned christening comes shortly after new mom Meghan made a rare public appearance this weekend, joining Harry for the first Major League Baseball game in London.
It was Meghan's third public appearance since Archie was born, and the duchess wore a Stella McCartney dress and flat shoes.