"I’m so proud and honored to have been chosen by the Duchess of Sussex to make her evening gown and represent British design," McCartney told ET on Saturday.
The elegant, hip-hugging lily white dress -- made of silk crepe --featured a high neck and exposed shoulders, as well as an open back.
McCartney added that getting the opportunity to design the incredible ensemble has "truly been one of the most humbling moments of my career and I am so proud of all the team on this stunning royal day."
Markle looked radiant as she left Windsor Castle alongside her tuxedo-clad new husband. The pair hopped in a silver blue Jaguar E-Type Concept Zero, en route to the reception at Frogmore House.
The Duke and Duchess of Sussex depart Windsor Castle for a reception hosted by The Prince of Wales at Frogmore House, in a silver blue Jaguar E-Type Concept Zero. This vehicle was originally manufactured in 1968, and has since been converted to electric power #RoyalWeddingpic.twitter.com/hRrxEUlFlJ
This evening's reception will have the bride and groom's close family and friends in attendance, and will include a speech from Meghan. This will be the first time she's spoken publicly as the Duchess of Sussex. The title of Duke and Duchess of Sussex was officially bestowed upon the couple by the Queen just before they tied the knot.