The Prince, 33, declared that he is "thrilled" as he and the 36-year-old American actress posed for an open-air photocall in the Sunken Garden at Kensington Palace.
A beaming Ms Markle, in a white belted coat, clutched Harry's hand with both of her hands as they posed briefly and showed off her diamond engagement ring - designed by the prince himself.
The two outside stones are diamonds from the personal collection of his mother - the late lady Diana. At the centre is a diamond from Botswana, a country that holds special significance for Harry who has visited many times since he was a child.
According to a statement by the Clarence House, the couple, who have been dating for 16 months, will marry in the spring 2018. However, many anticipate that the wedding will not be in April as Harry’s sister-in-law - Duchess of Cambridge is to give birth to her third child.