While they appeared at a private Buckingham Palace garden party three days after they Wednesday, Saturday afternoon's outing was the first time the former actress has been on full show as a royal.
The massed bands of the Household Division will provide musical backing during the day and also taking part is the King's Troop Royal Horse Artillery who, following the parade, will fire a 41-gun salute in Green Park to mark the Queen's official birthday. Kate Middleton, the Duchess of Cambridge, immediately knelt down to comfort her then held her as the parade continued.
Waving to crowds alongside the Duchess of Cornwall, Kate looked radiant in a frock from one of her favourite designers, Alexander McQueen.
Charanpreet Singh Lall, 22, was among more than 1,000 soldiers who participated in the ceremony attended by the Queen and members of the royal family, including the newly married Duke and Duchess of Sussex, Prince Charles and the Duke and Duchess of Cambridge.
Prince Charles, Colonel of the Welsh Guards, Princess Anne, Colonel of the Blues and Royals, and the Duke of Cambridge, Colonel of the Irish Guards, all followed the Monarch closely behind.
Meghan Markle is still breaking protocol despite her newly minted royal status.
The ceremony originated from traditional preparations for battle. She is the Queen's eldest great grandchild.
The young royal took a tumble up on the Buckingham Palace balcony while celebrating Queen Elizabeth's birthday. Although Queen Elizabeth already turned 92 on April 21, the royals understandably prefer to party and socialize in warmer weather.
Fans couldn't take their eyes off the 7-year-old, who amazingly deadpanned to the camera as she silenced Prince George with her hand over his mouth.
Matching their mother's color scheme, Charlotte wore a patterned blue dress along with a red bow in her hair.
Meghan, the new Duchess of Sussex, who has been welcomed into the Royal Family with open arms, has a busy week of appearances ahead.
He said: "I'm quite proud and I know that a lot of other people are proud of me as well".