Admiral Sir Tony Radakin has been appointed as the new Chief of the Defence Staff.
The current head of the Royal Navy is set to take up the role on 30 November, replacing General Sir Nick Carter – who had been expected to retire in June but was asked by Boris Johnson to stay in post until late 2021.
He is the first naval officer to be appointed Chief of the Defence Staff since Admiral Sir Michael Boyce, who was in post between 2001 and 2003.
Prime Minister Boris Johnson said he was "delighted" to announce Admiral Radakin as the next Chief of the Defence Staff.
"He has proven himself an outstanding military leader as First Sea Lord and Chief of the Naval Staff and I have every confidence he will be an exceptional Chief of the Defence Staff.
"Under his command we have more Royal Navy sailors on the front line, more warships at sea – including our two world class aircraft carriers – and we are leading a shipbuilding renaissance which is creating jobs and protecting lives around the UK.
"Admiral Tony will lead the Armed Forces at a time of incredible change while upholding the values and standards that they are respected for around the world."
Admiral Radakin who has previously served in numerous conflict zones, including the Falklands and Iraq said he was "humbled to have been selected in a time of enormous change".
Further adding that "It will be an immense privilege to lead our outstanding people who defend and protect the United Kingdom".
Watch: Admiral Sir Tony Radakin – a new man at the head of the UK Armed Forces.
As head of the Navy, he helped negotiate the recent Aukus deal, a pact between the UK, US and Australia to provide a fleet of nuclear-powered submarines for the Royal Australian Navy.
He also oversaw the two Queen-Elizabeth class aircraft carriers being declared operational, with HMS Prince of Wales announced ready for operations last week, and the launch of the UK Carrier Strike Group (CSG21) deployment earlier this year.
In his statement posted to Twitter, Adm Radakin added that the Prime Minister and the Defence Secretary, "have demanded reform and we must seize the opportunity the government has given us and ensure we are a global force delivering for Global Britain".
Defence Secretary Ben Wallace said the Royal Navy chief "brings an unparalleled wealth of experience to the role at a time of significant change for the Armed Forces".
"We are modernising to address the challenges posed by an increasingly unstable world and I know he will lead the Armed Forces with distinction in his new post."
Admiral Radakin was selected from a reported five-man shortlist, which is also thought to have included the heads of the British Army, RAF, Strategic Command and three-star military official Vice-Admiral Sir Ben Key – who recently led the UK's evacuation from Afghanistan.
Candidates for the outgoing Defence Chief's job had interviews with Defence Secretary Ben Wallace last month followed by interviews with the Prime Minister before he submitted his choice to the Queen, who ultimately made the appointment.
In a tweet, the Chief of the General Staff, General Sir Mark Carleton-Smith, wished Admiral Radakin "many congratulations" on his appointment as Chief of the Defence Staff.
He added: "The Army wishes him the best of luck in his important role."