This morning, Queen Elizabeth has made her grandson a Duke while also awarding him separate Scottish and Northern Ireland titles.
Markle becomes the first woman ever to hold this title.
The titles echo those bestowed on Prince William and Kate Middleton on the day of their marriage, when the Queen announced that they would become the Duke and Duchess of Cambridge.
Buckingham Palace said in a statement this morning: "The Queen has today been pleased to confer a Dukedom on Prince Henry of Wales. His titles will be Duke of Sussex, Earl of Dumbarton and Baron Kilkeel.
"Prince Harry thus becomes His Royal Highness The Duke of Sussex, and Ms. Meghan Markle on marriage will become Her Royal Highness The Duchess of Sussex."
Harry becomes only the second Duke of Sussex in the history of the British royal family. The previous Duke of Sussex was Prince Augustus Frederick, the sixth son of King George III and Queen Charlotte, who attained the title upon his birth in 1801.
As the New York Times notes, the previous Duke of Sussex was viewed dimly by the throne, then held by Queen Victoria, for his progressive views. He was married twice, but neither wives were offered the title Duchess of Sussex.
Kensington Palace announced yesterday that Prince Charles, the Prince of Wales, will be walking Markle down the the aisle at St. George's Chapel in Windsor Castle today. Her father, Thomas Markle, will not be attending the ceremony due to poor health.
Earlier this week, Markle also revealed her bridal party, which includes 10 royal children and her good friend Jessica Mulroney.