He was an Army officer, but he has so far been in civilian dress for official events, including walking behind his grandmother’s coffin on Wednesday when it was carried to Westminster Hall to lie in state.
But the Daily Mirror said palace officials have had a change of heart, with one source saying “common sense has prevailed”.
Rehearsal at dawn for Queen Elizabeth's funeral - in pictures
An exception has also been made for the disgraced Duke of York, who is no longer a working royal but will wear his military uniform as a “special mark of respect” for the queen when he stands guard around her coffin during a vigil with his siblings on Friday evening.
On Monday, Prince Harry wrote of his special memories of the queen attending his passing-out parade in 2006 when he became an officer in the British Army.
He told of his “first meeting” with his grandmother as “my Commander-in-Chief”, and is believed to have been referring to the occasion when she made him grin and blush as she reviewed the cadets.
Buckingham Palace has been contacted for comment.