Camilla — who is to be queen consort when her husband, Prince Charles, becomes king — selected her stepdaughter-in-law for the significant photoshoot. The royal guest edited the July issue of the publication, marking her 75th birthday on July 17.
In the relaxed image, Camilla is seen in a garden at Ray Mill House in Lacock, Wiltshire, which is where she lived before officially moving to Clarence House with Prince Charles and has been described as her "retreat".
She is sat on a bench, wearing a blue floral dress and cardigan, holding a basket of pelargonium flowers, which look ready to be planted.
The special edition of Country Life is being released as the magazine celebrates its 125th year.
Mark Hedges, editor-in-chief of Country Life magazine, said: “We are thrilled to have our guest editor captured so magnificently by royal photographer the Duchess of Cambridge.
“We understand this is the first time a formal portrait of the Duchess of Cornwall has been taken by the Duchess of Cambridge for a magazine and we are honoured to have been chosen to be the first to publish this beautiful photograph.
“The photographs are superb and we would be delighted to offer the Duchess of Cambridge another commission.”
A second photo by Kate appears inside the magazine, a more informal shot of Camilla walking through forget-me-nots at her country home.
This is not the first time the British royal family has used pictures taken by the duchess, who is a keen amateur photographer and patron of the Royal Photographic Society. They frequently share images she has taken of her children Prince George, 8, Princess Charlotte, 7, and Prince Louis, 4, alongside husband Prince William.
On Princess Charlotte's seventh birthday in May, the family shared photos of her smiling in the garden, including one with their family dog, Orla, a black cocker spaniel. The images were all credited to the Duchess of Cambridge.
What is Ray Mill House?
The photographs of Camilla were taken at Ray Mill House, her property in Lacock, Wiltshire.
She bought the six-bedroom house after her divorce from Andrew Parker Bowles in the mid 1990s.
See Camilla, Duchess of Cornwall's style evolution:
— Additional reporting from PA Media