Kensington Palace said the couple chose to tie the knot on a Saturday because "they felt it would give the public the greatest opportunity to watch, come out, support and get involved".
Ms Markle's parents Thomas Markle and Doria Ragland wished their daughter and Harry "a lifetime of happiness", adding: "We are incredibly happy for Meghan and Harry".
Markle is planning to get baptised in the Church of England ahead of her marriage and will apply for British citizenship, as well as giving up her global charity campaigning.
The royal family are paying for the wedding, including the church service, the music, the flowers and the reception.
The couple confirmed to the world that they are to be married in spring 2018 and has now confirmed that she he will be spending Christmas with the royals.
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The weekend wedding date presents a diary clash for Harry's brother, Prince William, who has been president of England's national soccer association since 2006; it coincides with the final of the FA Cup, England's top soccer cup competition, which William usually attends to present the trophy to the winning team.
"They will be making sure it reflects who they are as a couple", he said. "She held out her hand & said 'Hi, I'm Meghan.' She was unbelievably lovely, and Harry looked so proud". "It has been wonderful getting to know Meghan and to see how happy she and Harry are together".
Harry's communication's secretary Jason Knauf said Windsor was a "very special place" for Harry, and that he and Ms Markle had spent time there together during their 16-month romance.
Kate was not invited to join Prince William in 2010 with his family - despite the couple announcing their engagement a month before.
George's Chapel has hosted many royal weddings.
The newlyweds are tipped to become the Duke and Duchess of Sussex.
The palace said the Queen has granted permission for the wedding to take place at the chapel.