The Love Actually star and two-time Oscar nominee wore a yellow tweed blazer and skirt from Chanel, complete with a matching top hat.
Knightley joins a host of other British actors, musicians and other celebrities who have been awarded the honour, including James Corden, Victoria Beckham and Eddie Redmayne.
Knightley recently came under fire after she criticised the pressures placed on women following the Duchess of Cambridge's ultra-polished appearances outside the Lindo Wing of St. Mary’s Hospital just hours after giving birth.
The actress welcomed her daughter, Edie, just one day before Princess Kate gave birth to her second child, Princess Charlotte, back in 2015.