The 30-year-old Apache pilot, who has undertaken two operational tours of Afghanistan, will first spend four weeks seconded to the Australian Defence Force and then undertake a tour of New Zealand before completing his operational services in June, Kensington Palace said.
In his statement, the fourth in line to Britain's throne said he was at a "crossroads" and quitting the Army had been a "really tough decision".
"From learning the hard way to stay onside with my Colour Sergeant at Sandhurst, to the incredible people I served with during two tours in Afghanistan, the experiences I have had over the last 10 years will stay with me for the rest of my life.
"For that I will always be hugely grateful."
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While in Australia, the prince will spend time at an army barracks in Darwin, Perth and Sydney where he will carry out unit-based activities, training exercises and domestic deployments.
After his stint in Australia, he will undertake an official royal tour to New Zealand.
When he leaves the Army in June, he will do voluntary work with a conservation project in Africa and with disabled veterans back in the UK with the ministry of defence Recovery Capability programme.
Prince Harry, or Captain Harry Wales as he was known in the Army, started his full-time military duties as an officer cadet at the Royal Military Academy Sandhurst in May 2005.
He was commissioned as an Army officer in April 2006, joining the Household Cavalry (Blues and Royals).
He began training as an Army Air Corps pilot in January 2009, becoming a fully operational Apache attack helicopter pilot in February 2012.
Later in 2012, he undertook an operational tour of Afghanistan as an Apache pilot.
Gen Sir Nicholas Carter, Chief of the General Staff and the professional head of the Army, said, "Captain Harry Wales, as he is known affectionately in the Army, has achieved much in his 10 years as a soldier."
"He has been at the forefront throughout his service. He has insisted on being treated the same as his peers."