Guests at her wedding to Prince Harry will also have to be on best behaviour, abiding by the strict protocols that underpin the pomp and ceremony which give the family its worldwide appeal.
Here are the complex customs that Markle and her guests need to navigate, according to royal etiquette expert William Hanson.
- Bowing and curtseying -
When meeting royal family members, men are expected to bow from the neck and women curtsy, a formality that even world leaders have sometimes found a challenge.
"It is not a curtsey going right down to the floor because you may never get back up, it is a bob of the head, hands behind the sides, one foot behind the other. Bend of the knees, keeping your back straight," explained Hanson.
Markle will be expected to quickly learn the protocol, with the help of courtiers and close family members.
If she is with Prince Harry, Markle takes on her husband's status, with royals below Harry in seniority expected to curtsey before her.
"But if Meghan is walking down the corridor on her own and she bumps into Princess Beatrice, Beatrice is a blood royal and so Meghan will have to curtsey for Beatrice. It's confusing," Hanson said.
For novice royal watchers, there is a simple way of knowing who fits where in the royal hierarchy.
"You can sort of work it out by when people arrive at events," said Hanson. "The less important you are, the earlier you arrive."
- Introductions -
Pop star Ed Sheeran gave an example of how not to greet a member of royalty when he recently placed his left hand on Prince Charles's right arm as they shook hands.
"Don't use your left hand, it just stays by your side," said Hanson. "That was a breach of protocol".
When talking to the Queen, she should be called "your majesty" at first, and then "ma'am".
"It's ma'am as in ham, not ma'am as in farm," explained Hanson.
- Bridal attire -
Having been married already, speculation abounds as to whether Markle will wear a full bridal gown, or opt for less formal day dress.
"If it is a wedding dress, I don't think it's going to be big," said Hanson.
Tiaras are only allowed for married women.
If Meghan is to wear one on the day after her vows, she would not be able to buy one herself. It would have to be a gift from the royal collection, unless she already has a family heirloom.
"A gift as in 'we will have it back'," he added.
Harry is expected to wear "morning dress", which usually consists of a tailcoat, a bright waistcoat and tie, although he could wear his military uniform.
"Prince William in his military uniform in 2011, it looked beautiful, it was so Cinderella," said Hanson.
- Guest dress code -
The dress code on the invitation reads: "Uniform, Morning Coat, Lounge Suit, Day Dress with hat".
The etiquette expert said it was "interesting" that the invitation had spelled out the need for a hat, pointing out some high profile faux pas from the 2011 wedding of Prince William and Catherine Middleton.
Samantha Cameron, wife of then prime minister David Cameron, wore no hat, instead of wearing jewels in her hair.
"Reportedly she didn't wear tights either, as the wife of a prime minister and the daughter of a baronet, she should know better."
Football legend David Beckham was also guilty of multiple protocol breaches with his morning dress.
"The collar was wrong, it was a winged collar, it should have been a turned-down collar.
"And everything matched, it's morning dress, not a morning suit.
"He was wearing a medal; he was wearing it on the wrong side and secondly the invitation did not say 'with decorations'. He shouldn't have worn it."
- Hand holding? -
Harry and Meghan have been tactile during public engagements -- unusual for royal family members.
"It will be interesting to see whether Harry and Meghan continue to hold hands at official engagements," said Hanson.
"It's just not a British thing, it's a form of emotion and in Britain we normally show emotion to dogs and horses."//AFP