She appeared to pay a subtle tribute to her 92-year-old grandmother with her choice of outfit for the annual event.
Eugenie, 29, wore Erdem’s floral-print silk crepe de chine ‘Bernette’ dress, which was inspired by Her Majesty’s style in the 1950s.
While the £831 frock is now sold out, according to Net-a-Porter, the Canadian-born designer delved “deep into Queen Elizabeth II's past for his Spring '18 collection” and was “particularly drawn to her style in the '50s.”
The royal first debuted the outfit at Royal Ascot last year. She married long-term boyfriend Jack Brooksbank at St George’s Chapel last October.
Erdem has long been a favourite designer of the Royal Family - the Duchess of Cambridge and the Duchess of Sussex have also sported his creations.
He was one of the frontrunners to design Meghan’s wedding dress for her and Prince Harry’s wedding last May.
At the service, the Queen handed out commemorative coins, known as Maundy Money, to senior citizens in recognition for their contribution to community and to the church.
The gifts the monarch hands out match her age; she turns 93 on Sunday, so she distributed 93p worth of Maundy money to 93 men and 93 women.
READ MORE: How the royals celebrate Easter
Each recipient is given two purses. The money in the White Purse includes 1, 2, 3 and 4 silver penny pieces, the sum equals the number of years of the Monarch’s age.
The Red Purse contains a £5 coin, commemorating the 200th anniversary of Queen Victoria's birth & a 50p coin portraying Sherlock Holmes.
The Queen stood out in a buttercup yellow coat, a matching hat and floral dress for the service.
She and her granddaughter were both given nosegays made up of daffodils, primroses, stocks, purple statice, freesias, ivy, hebe and the herbs rosemary and thyme.
Her Majesty will attend the Easter Sunday service at St George’s Chapel, with other members of the Royal Family.