Markle, 36, joined Harry, 33, at the Commonwealth Heads of Government meeting in London.
The conference, which brings together heads of state and delegates from the 53 member nations of the Commonwealth, is highly significant, with Markle attending her first major diplomatic event on behalf of the royal family.
On Monday, Queen Elizabeth named Harry the Commonwealth Youth Ambassador, which will form a large part of his and Markle's work after they are married on May 19.
More than 60 percent of the Commonwealth's 2.4 billion people are under the age of 30. Harry's work as ambassador will focus on “supporting the aspirations of young people,” according to a statement released by Buckingham Palace.
Harry discussed his new role with excitement in a keynote speech he delivered Monday.
"In my new role, I will work to support the Queen, my father The Prince of Wales, and my brother William, all of whom know that young people are the answer to the challenges of today," he said. "I am also incredibly grateful that the woman I am about to marry, Meghan, will be joining me in this work, of which she too is hugely excited to take part in."
It is unusual for Markle, someone who has not yet married into the royal family, to be involved in such a high-profile event as the Commonwealth Heads of Government summit.
The event takes place every two years to discuss the issues facing the Commonwealth's 2.4 billion citizens.
Markle stood out in a beautiful, pin-striped sundress by Altuzarra and a cross-body bag by Oroton, an Australian brand she may have chosen in a nod to the Commonwealth.
Tomorrow, the couple will make their second appearance at the summit.
Harry and Markle will take part in a reception to promote women’s empowerment, an issue that has been of great interest to Markle in her previous humanitarian work. The reception will feature charities and organizations that work to promote global gender equality through girls’ education.
Last stages of wedding planning
The couple are in the last stages of planning for their wedding at Windsor Castle on May 19.
Markle has been attending secret fittings with her dress designer and has been working with her close friend and style adviser, Jessica Mulroney, to put the finishing touches on her wedding at Windsor Castle and reception at Frogmore House.
Harry and Markle have already selected an American baker, Claire Ptak, who now owns a London bakery, to create a lemon elderflower cake.
They have also chosen Alexi Lubomirski, who took their stunning engagement photos, to shoot the photographs on their wedding day.
Harry has been traveling around the U.K. with Markle to meet as many as possible of the people she will one day represent.
He is also introducing her to many of the charities that will form the core of Markle's work when she joins the Royal Foundation as the fourth patron following their marriage.