Admiral Sir Tony Radakin, formerly First Sea Lord and Chief of the Naval Staff, will take over from General Sir Nicholas Carter as Chief of the Defence Staff. The 55-year-old, from Oldham, Lancashire, has enjoyed a glittering Navy career since 1990.
He played a key role in the Iran and Iraq tanker war, as well as countering smugglers in Hong Kong and the Caribbean.
The father of four has also completed three command tours in Iraq, both ashore and at sea.
His appointment by the Prime Minister, approved by the Queen, starts on November 30.
Boris Johnson said: “Admiral Tony will lead the Armed Forces at a time of incredible change while upholding the values and standards they are respected for around the world.
“I know he will bring drive and dedication to the job and I look forward to working with him.” Defence Secretary Ben Wallace hailed Sir Tony’s “unparalleled wealth of experience”.
Mr Wallace said: “We are modernising to address the challenges posed by an increasingly unstable world and I know he will lead the Armed Forces with distinction.
“Admiral Tony has been an outstanding First Sea Lord and Chief of Naval Staff during a period of transformation for the Royal Navy. That includes the inaugural voyage of HMS Queen Elizabeth, which set sail in May.
“There is much to be done, at home and abroad, as the threats against the UK and our allies are growing.”
Admiral Sir Tony said: “I am humbled. It will be an immense privilege to lead our outstanding people who defend and protect the UK. I would like to thank General Sir Nick Carter for his leadership and wise stewardship of the UK’s Armed Forces over the last three years.
“The Government has given us clarity and additional resource to counter the threats we face as a nation. It is now time to deliver.”