The former Suits actress was accompanied by her fiancé, Prince Harry, and wore a chic white coat by designer Amanda Wakeley and a beret by Stephen Jones.
Pregnant Catherine Middleton attended the event with her husband, Prince William, and showed off her baby bump in a classic navy coat and matching navy hat.
Prince Charles and Camilla were also at the annual church service, which included a performance by singer Liam Payne, and a reflection by Dr. Andrew Bastawrous.
Kensington Palace commented shared a photo of the royals at the event, commenting: 'The Duke and Duchess of Cambridge, Prince Harry and Ms. Meghan Markle joined The Queen and other Members of The Royal Family at service at Westminster Abbey, organised by The Royal Commonwealth Society, to celebrate Commonwealth Day 2018.'