The First Sea Lord and Chief of the Naval Staff (1SL/CNS) is a statutory position in the British Armed Forces usually held by a four star admiral. As the highest-ranking officer to serve in the Royal Navy, the chief is the principal military advisor on matters pertaining to the navy and a deputy to the Secretary of State for Defence. In a separate capacity, the CNS is a member of the Chiefs of Staff Committee and, thereby, a military advisor to the National Security Council, the prime minister and the monarch. The First Sea Lord is typically the highest-ranking officer on active duty of the Royal Navy unless the Chief of the Defence Staff is a naval officer. Admiral Ben Key was appointed First Sea Lord in November 2021.

The Defence Council of the United Kingdom is the supreme governing body of the British Armed Forces. It was established by the Defence Act 1964, which statutorily delegated the military authority of the Crown, as head of the Armed Forces, to the Defence Council. It has the power of "command and administration" over the military.