The royal wore a summery Emilia Wickstead dress with a bespoke hat by milliner Philip Treacy and nude Gianvito Rossi pumps. She borrowed Queen Elizabeth II's pearl earrings for the occasion.
The duchess wasn't the only royal in attendance, as she was joined by husband, Prince William, and family members, including the Duke and Duchess of Sussex, Zara and Mike Tindall and Princesses Beatrice and Eugenie.
The service marked Meghan, Duchess of Sussex's first public appearance during the jubilee celebrations. For the event, she wore a look by Dior, including a bespoke belted coat, with a co-ordinated white hat and suede pumps by the French fashion house. Her look was accessorised with a Cartier Love bracelet.
Also in white was Camilla, Duchess of Cornwall, who wore an embellished brush silk coat dress with a wide-brimmed white hat. Sophie, Countess of Wessex, wore a metallic rose gold Suzannah London dress, with a co-ordinated hat. The look is her second pink ensemble of the weekend, after wearing a pink gingham dress to attend Trooping the Colour on Thursday.
The younger generation of royals seemed to agree on a vibrant dress code, as the queen's granddaughters, Zara Tindall and Princesses Beatrice and Eugenie wore a selection of vibrant shades.
Tindall, who was joined by husband ex-rugby player Mike Tindall, wore a fuchsia dress by Laura Green London, and Princess Eugenie wore an orange Emilia Wickstead ensemble with a black hat. Her sister, Princess Beatrice wore a powder-blue Beulah London dress and hat, with pearl button detail.
Prime Minister Boris Johnson and former prime minister David Cameron were among the politicians in attendance. Johnson's wife, Carrie Johnson, wore a striking red dress and a hat with red floral embellishment. Samantha Cameron wore a blue patterned dress by her own fashion label, Cefinn.
Day one of the platinum jubilee
The thanksgiving service took place on day two of the platinum jubilee celebrations. On the first day, royals attended Trooping the Colour, a military parade in central London.
Kate, Duchess of Cambridge, chose a white dress coat, thought to be by British design house Alexander McQueen, with a black and white Philip Treacy hat, a pair of sapphire earrings that belonged to Diana, Princess of Wales and a clutch bag by Scottish brand Strathberry.