The Secretary of State for War, commonly called War Secretary, was a secretary of state in the Government of the United Kingdom, which existed from 1794 to 1801 and from 1854 to 1964. The Secretary of State for War headed the War Office and was assisted by a Parliamentary Under-Secretary of State for War, a Parliamentary Private Secretary who was also a Member of Parliament (MP), and a Military Secretary, who was a general.

The position of Secretary of State for War was first held by Henry Dundas who was appointed in 1794. In 1801 the post became that of Secretary of State for War and the Colonies. The position of Secretary of State for War was re-instated in 1854 when the Secretary of State for the Colonies was created as a separate position.

In the nineteenth century the post was twice held by future prime minister Henry Campbell-Bannerman. At the outset of the First World War, prime minister H. H. Asquith was filling the role, but he quickly appointed Lord Kitchener, who became famous while in this position for Lord Kitchener Wants You. He was replaced by David Lloyd George, who went on to become prime minister. Between the World Wars, the post was held by future prime minister Winston Churchill for two years.

In 1946, the three posts of Secretary of State for War, First Lord of the Admiralty, and Secretary of State for Air became formally subordinated to that of Minister of Defence, which had itself been created in 1940 for the co-ordination of defence and security issues.

In the 1960s, John Profumo held this post at the time of the Profumo affair.

On 1 April 1964, with the creation of a new united Ministry of Defence headed by the Secretary of State for Defence, the three service ministries as well as the post of Minister of Defence as created in 1940 were abolished.

• Secretary at War