Her dress, although casual and simple in its shirt-style tailoring, was rich in detail with subtle embroidery around the waist and was finished off with fine white buttons.
Therefore, while Harry and Meghan's choice of tour is perfectly normal, it is a royal first for the traditional family, with the Queen only making her first visit to the region in 2011, after being monarch for over half a century.
At the Trooping the Colour earlier this month, she looked chic in a dress by Carolina Herrera and another Treacy hat.
Markle's dress for Ascot was more covered-up than we often see her - the Duchess loves an open neckline - but that's due to the conservative dress code of the royal-sponsored event.
Dettori, 47, kissed Meghan's hand as she presented him with his trophy for riding the favourite, Without Parole, to victory in the St James's Palace Stakes.
Clare Waight Keller, the creative director of Givenchy who designed the dress for the formal wedding, carriage ride and daytime reception, said previously: "I think every bride is unique".
But Meghan is diving in heard-first, keen to experience a day at the races with her new extended family.
Dressed in a cream lace Dolce & Gabbana dress and ivory fascinator, the Duchess of Cambridge looked elegant pairing the look with diamond drop earrings and nude heels.
Click on the gallery above for more pictures of the Royals at Ascot.
But it also marked the last moment she could indulge in the full joy and self-expression of fashion, the dress designer has said.
The couple du jour arrived in onto the course in a carriage accompanied by Harry's uncle Prince Edward and Sophie, the Countess of Wessex. Kensington Palace said that the royal couple will travel to Dublin for two days starting on July 10.