Among the first of the couple's guests to arrive in London was "Suits" co-star Gabriel Macht, who plays Harvey Specter.
The 46-year-old American actor and his actress wife, Jacinda Barrett, have been taking in the sights around the British capital, posting pictures on their Instagram accounts.
In one, Barrett is perched outside Buckingham Palace receiving a kiss from her four-year-old son. Barrett also starred on "Suits" as Specter's one-time love interest, Zoe Lawford, between 2012 and 2013.
Their co-star Sarah Rafferty, who plays executive assistant Donna Paulsen, has been traveling in Europe with her family, posting family photos from Paris on Instagram in recent days.
Rick Hoffman, who stars in the show as Louis Litt, posted a video on Instagram, telling fans he was "excited" to be "heading east for some special event."
Other former co-stars and close friends of Meghan, including Patrick J. Adams, Abigail Spencer, Gina Torres and Amanda Schull are also expected to attend.
Meghan's mother, Doria Ragland, arrived in London on Wednesday, British media reported. She is due to spend time with the royal family ahead of the ceremony on Saturday.
One confirmed no-show will be Meghan's father Thomas Markle, who has had to pull out over health problems.
"Sadly, my father will not be attending our wedding. I have always cared for my father and hope he can be given the space he needs to focus on his health," Meghan Markle said Thursday in a statement pro by Kensington Palace.
Thomas Markle, who has been the subject of a staged photo controversy in recent days, was due to walk his daughter down the aisle. It is unclear who will now take on that duty.