Her Majesty made the announcement in a letter to the Privy Council, her official group of advisors.
It read: "I declare My Consent to a Contract of Matrimony between My Most Dearly Beloved Grandson Prince Henry Charles Albert David of Wales and Rachel Meghan Markle, which Consent I am causing to be signified under the Great Seal and to be entered in the Books of the Privy Council."
The 91-year-old monarch did the same for Prince William and Duchess Kate ahead of their royal wedding in April 2011.
The announcement arrives just a few days after the Queen's first public appearance with Meghan at a Commonwealth Day church service at Westminster Abbey on Monday.
The former actress arrived on the arm of her husband-to-be, looking typically put-together in a cream tailored by Amanda Wakeley and a matching beret by Stephen Jones. She accented the subdued ensemble with dark navy suede pumps and a mini navy leather bag.
Following the event, the young royals spent some time with those who gathered from far and wide to catch a glimpse of their outing.
Meghan, 36, is stepping into the role of the people's princess with ease.
Talking to David Swindells, she said: "The service was beautiful, especially the choir and the music."
Charmed by their conversation, the teacher admitted, "She was very personable. I think she'll be a great addition."
WATCH: Harry, Meghan, Wills and Kate attend the Commonwealth Day church service. Post continues...
Another attendee, Ms Hartley, also shared a snippet of her moment alongside the royal-to-be.
"She was saying what a lovely service it had been and her first service at Westminster Abbey. We congratulated her on her engagement."
"She was delighted and said she was 'very, very excited' about her wedding."
Ms Hartley added: "She stayed chatting with us for quite a while - what a lovely, lovely lady."
As Kensington Palace recently announced, following the ceremony, the newlyweds will undertake a tour of the town as their first trip as man and wife to greet well-wishers from all over the world who have come to see them.
It will no doubt remind fans of similar scenes that played out during Prince William and Duchess Catherine's 2011 wedding.
WATCH: Relive the magic from Prince William and Duchess Catherine's wedding day. Post continues…
There's also speculation the 36-year-old might be walked down the aisle by none other than Prince William.
According to The Sun, Prince Harry's big brother may step up for the important moment as Meghan's two closest male relatives -- her father and half-brother -- may not be at the royal wedding.
Not long to go now!