The Duchess of Cornwall has been made a Dame Grand Cross, the highest female rank in the Royal Victorian Order.
The announcement by Buckingham Palace comes as Camilla and the Prince of Wales celebrate their seventh wedding anniversary.
A Buckingham Palace spokeswoman said Camilla, 64, would be invested with the insignia of her rank at a later date.
Appointments to the Royal Victorian Order are made by the Queen independently of 10 Downing Street.
The Order was founded in April 1896 by Queen Victoria as a way of rewarding personal service.
The duchess has become patron of a number of organisations and has travelled extensively with the prince on official visits.
BBC correspondent Fiona Trott commented: "As Charles's second wife, the duchess's involvement in royal engagements was gradual. But now, she's often seen at the Queen's side.
"It's likely that Camilla's award is in recognition of her many royal engagements at home and abroad over the past seven years and is an indication of her importance within the Royal Family."