And now the newlyweds, who married in Windsor last May, are just weeks away from welcoming their first child.
As the nation waits for the Queen and Duke of Edinburgh's eighth grandchild to arrive, here's everything we know about royal baby Sussex.
When is the Royal baby due?
Although Kensington Palace has only said the royal baby is due in the spring, six-month pregnant Meghan let slip during an engagement in Birkenhead earlier this year that she is due at the end of April or early May.
The couple announced their pregnancy to family and friends at Princess Eugenie’s wedding in October, just days before their royal tour of Australia, New Zealand, Fiji and Tonga.
This means he or she could easily be born on the same day as great-grandmother the Queen, who will celebrate turning 93 on April 21.
If the couple do know the gender, they're keeping it very quiet. They recently said they'd be “thrilled” with a baby boy or girl.
Where will the Duchess of Sussex give birth?
No one knows for sure, but staff at the Lindo Wing at St Mary’s Hospital in Paddington, London, have been advised not to take holiday in the spring, sparking speculation the Duchess plans to give birth there.
Contrary to earlier reports the former American actress plans to give birth on the NHS, she may instead follow in the footsteps of the Duchess of Cambridge, who had her three children at the same private maternity unit. Princess Diana also gave birth to Harry there in 1984.
A source told the Telegraph: “Staff at the Lindo Wing have been asked not to take holiday in April. Everyone thinks it’s got something to do with the royal baby but no one is confirming anything.”
It had been reported that Meghan, 37, planned to give birth on the NHS at Frimley Park Hospital in Surrey, because it is seven miles closer than the Lindo Wing to Frogmore Cottage in Windsor, where the Sussexes are due to move to this year.
Giving birth in the Lindo Wing
The £6,000-a-night Lindo wing offers a “five-star” birthing experience with expectant mothers accommodated in spacious private rooms with en-suite bathrooms.
Patients are invited to pick their meals from lavish a la carte menus – including a wine and champagne list – and are offered a celebratory post-labour afternoon tea.
The first night in Lindo wing costs £5,900 for the normal delivery package and then every additional night is charged at £1,175.
Patients can pay extra for a deluxe package, where the rooms are slightly bigger, which costs £6,275 for the first 24 hours and £1,550 for extra nights.
Read more about the Lindo Wing here.
What will the royal baby be called?
There will be much suspense as to what the Duke and Duchess of Sussex will call their baby.
The youngster will be born into the British royal family, where tradition is an intrinsic part of the Windsors' lives. If they go classic, something like Alice, Mary, Elizabeth or Victoria for a girl, and Philip, Frederick, Charles, Arthur, Edward or James for a boy are possibilities.
But the pair are also forward-thinking royals, and the duchess has her own American upbringing to draw on.
Canadian-born Autumn Phillips, and husband Peter Phillips, opted for a non-traditional name for their daughter Savannah - the Queen's first great-grandchild - in 2010.
In the US, the most popular name for a baby girl is Emma and Liam for a baby boy. In the UK, the most popular name for a girl born in 2017 was Olivia, and for a boy Oliver. In short, it's anyone's guess.
Where will the baby fall in the line of succession?
Seventh in line, which means it's highly unlikely the child will ever be monarch.
The baby will have three cousins: Prince George - a future king - and Princess Charlotte and Prince Louis, who are further up the line of succession, so it is a safe bet that the throne will stay on the Cambridge side of the family.
The baby will bump Harry's uncle, the Duke of York, into eighth place in the line of succession.
His daughter's Princesses Beatrice and Eugenie move into ninth and 10th place, and Prince Edward, Earl of Wessex - the Queen's youngest son - drops out of the top 10 for the first time to 11th in line.
What title will the new royal baby have?
The Duke and Duchess of Sussex's baby will not be a prince nor a princess unless the Queen steps in.
King George V - Harry's great great grandfather - limited titles within the royal family in 1917. This means the couple's first born, as a great-grandchild of the sovereign, is too far down the line of succession to be an HRH.
George V declared that: "the grandchildren of the sons of any such Sovereign in the direct male line (save only the eldest living son of the eldest son of the Prince of Wales) shall have and enjoy in all occasions the style and title enjoyed by the children of Dukes of these Our Realms."
The eldest son and heir apparent of a duke can use one of his father's lesser grade peerage titles by courtesy, according to Debrett's.
So a first son of Harry's would become Earl of Dumbarton - one of the subsidiary titles Harry received from the Queen on the morning of his wedding. A daughter would be Lady (first name) Mountbatten-Windsor, and any subsequent sons Lord (first name) Mounbatten-Windsor.
Will the baby have dual citizenship?
The Duke and Duchess could apply for their child to have dual US-UK citizenship.
The Duchess is in the process of becoming a British citizen - but it is not known whether she will hold dual nationality, and at present is still a US citizen.
According to the American Embassy in the UK, a child born outside of the US and in wedlock to a US citizen parent and a non US citizen parent, may acquire US citizenship at birth if the US parent lived in America for five years - two of which were after the age of 14.
Where will the family live?
The Duke and Duchess of Sussex are due to move into Frogmore Cottage in the grounds of Windsor Castle this year, however the property is still under-going extensive refurbishment.
Since 2017, the couple have been living at Nottingham Cottage, in the grounds of Kensington Palace near the Duke of Cambridge and his family, but the move means they will be 20 miles away from them.
Read more about Nottingham Cottage here.
Will the Sussex's hire a nanny?
Most likely. Harry has been close to all his nannies and it is likely he and Meghan will arrange for a nanny to care for their baby while they are on official engagements.
Kate and William have the help of their full-time live-in nanny Maria Teresa Turrion Borrallo. Meghan's close friend Jessica Mulroney had two nannies to help her with her twin boys and younger daughter.
The couple will almost certainly call upon the help of Meghan's mother Doria Ragland who will no doubt make frequent visits to London from her Los Angeles home to visit her grandchild.
Read more about what it's really like to be a royal nanny here.
Keep up to date with the Royal family by signing up to our weekly newsletter, Your Royal Appointment.