There is no indication of how many employees will be affected by the clampdown but courtiers are not forcing them to go "cold turkey".
As a "transitional measure", the smoking of e-cigarettes will be permitted in those designated areas for a further six months, until May 21 next year.
From May 22, however, Royal Household sites will be strictly smoke free. The policy covers Buckingham Palace, Windsor Castle, St James's Palace, Kensington Palace and the Palace of Holyroodhouse in Edinburgh.
Clarence House has been a smoking-free zone for many years because Prince Charles, whose home it is, hates the "filthy" habit.
One of the more high-profile royal smokers was the Duchess of Cornwall, who was said to have had a solid ten-a-day habit even though Charles loathed it.
According to friends, she finally gave up some 15 years or so ago with the help of an alternative health practitioner after developing rhinitis, an allergy that causes irritation in the eyes, nose and throat.
Former nanny Tiggy Legge-Bourke's constant smoking (she used to clamp a cigarette between her teeth even as she sped down the ski slopes) so annoyed Charles that he would banish her to the roof of St James's Palace to light up.
And Prince Harry has smoked since his early teens - a habit he picked up while a pupil at Eton. It is said that the 32-year-old prince can easily get through a packet of Marlborough Lights a day.
The Queen's father King George VI was also a heavy smoker, said to get through 50 cigarettes a day - even after tests suggested the presence of a malignant tumour in his left lung.
As shown recently in the TV show The Crown, he died, at the age of 56, on February 6, 1952 after suffering a coronary thrombosis - a fatal blood clot to the heart - soon after falling asleep.
He was also revealed to have been suffering from lung cancer.
Princess Elizabeth, who was at the Royal hunting lodge in Kenya, immediately became Queen at the age of 25.
Buckingham Palace told the Daily Mail: "Royal Household sites have been smoke free premises since November 21, 2016."
Officials indicated that the Queen's household already complied with the Health Act 2006, which prevents smoking in enclosed public spaces, including workplaces.
But following staff consultations it was decided to extended the ban to even long-standing designated smoking areas.
Harry might yet find himself an exception to the rule - apparently the policy does not cover private apartments and some self-contained staff accommodation, where others cannot be affected by their smoking.