Prince Harry was knighted by his grandmother, the Queen, in a private ceremony in Buckingham Palace on Thursday (4 June).
The prince, 30, was made a Knight Commander of the Royal Victorian Order (KCVO) for "services to the sovereign."
The honour, founded in 1896 by Queen Victoria, is a personal award given by British monarchs for service to them.
It is the only knighthood that can be awarded personally by the Queen rather than by ministerial recommendation.
Prince Harry announced in March he would leave the military in June after a decade of service, including two tours in Afghanistan.
He most recently completed a four-week secondment with the Australian Defence Force.
Prince Harry is a prominent supporter of charities such as Help for Heroes and ABF the Soldiers' Charity.
In 2014, he launched the Invictus Games, which are designed to use the power of sport to inspire recovery and support rehabilitation in injured members of the armed forces.
After leaving the army, the prince will volunteer with disabled veterans in the UK and a conservation project in Africa.
Harry has not made any long-term plans yet, but like his father and elder brother William, he has taken on more official duties as the 89-year-old queen scales back her workload.
According to the Telegraph, a royal source said the prince was "proud and pleased" to receive the honour, adding: "It is very significant for him personally."