Admiral Sir Tony Radakin will officially take over the role of Chief Of Defence Staff (CDS) in November, becoming Britain's most senior military official.
In taking over the role of CDS from General Sir Nick Carter, he will become the first military chief to come from the Royal Navy since Admiral Sir Michael Boyce in 2001.
Adm Radakin overcame competition from General Sir Patrick Sanders and General Sir Mark Carleton-Smith.
Defence Secretary Ben Wallace said he was "delighted" with the announcement and was quick to congratulate Admiral Sir Tony Radakin on his appointment as Chief of the Defence Staff.
Sir Tony Radakin will leave his role as First Sea Lord after he officially took over the position in 2019, succeeding Admiral Sir Philip Jones as Chief of the Naval Staff.
In his former role he commanded more than 30,000 men and women, more than 90 warships, nuclear submarines and support vessels, the helicopters and jets of the Fleet Air Arm and the elite Naval infantry of the Royal Marines.
Watch: Adm Radakin promised a "rich decade" for the Royal Navy.
Adm Radakin's career
After being commissioned in 1990, Adm Radakin's service has included security duties in the Falklands, NATO embargo operations in the Adriatic, and counter-smuggling in Hong Kong and the Caribbean.
He has also served three command tours in Iraq.
Adm Radakin has commanded from Lieutenant to Rear Admiral of ashore, afloat and international forces, including HMS Blazer and Southampton URNU (University Royal Naval Unit), HMS Norfolk, the Naval Training Team in Iraq, the Iraqi Maritime Task Force, Portsmouth Naval Base, and Commander of UK Maritime Forces and NATO's High Readiness Maritime Component Commander.
His staff appointments have mainly consisted of joint and defence roles, including operational planning at PJHQ (Permanent Joint Headquarters), two tours as a Military Assistant, and two tours involving financial, capability and strategic force development.
Previously, he worked as Chief of Staff of the Joint Forces Command from 2016-2018 and Second Sea Lord from 2018-2019.
While Navy chief, Adm Radakin has overseen the deployment of the UK's maiden Carrier Strike Group deployment, and the formation of AUKUS – a defence alliance with the US and Australia which will provide the latter with nuclear-powered submarines.
The outgoing First Sea Lord Admiral Tony Radakin became a Sir for his "relentless drive and clear vision, shaping every aspect of the Royal Navy".
The citation for his Knight Commander of the Most Honourable Order of the Bath (KCB) refers to the "seismic impact his improvements and innovations are having on the senior service".
He is president of the Royal Navy Squash Association and the UK Armed Forces Tennis Association and has even been known to accept challenges from cadets.