The Queen’s daughter will make military history by becoming the first woman to head the Royal Marines. Nephew Harry was stripped of the prestigious post after he married Meghan, Duchess of Sussex, and moved to the United States.
The Princess Royal now holds the honorary title of Admiral in the Royal Navy.
It is understood that her new job will be announced in August after official endorsement by the monarch.
The Royal Family has undergone a number of changes over the last few years with Prince Harry and his uncle Prince Andrew seeing all their honorary military titles removed.
Prince Charles has also assumed a leading role as the Queen, who celebrated her 96th birthday on Thursday, cuts back on public appearances.
A number of new military appointments are due to be announced by Buckingham Palace, including Princess Anne heading the marines and potentially at least two new Army roles.
Regiments including the marines, Grenadier Guards, Irish Rangers and Yorkshire regiment have been left without an honorary head after Harry and Andrew were removed from their roles.
Anne, 70, is known for undertaking a number of public engagements.
She already heads 10 regiments, including Colonel in Chief of the King’s Royal Hussars, the Royal Scots, The Gurkhas and the Royal Army Veterinary Corps.