Sir Percy James Grigg, KCB, KCSI, PC (16 December 1890 – 5 May 1964), often referred to as P J Grigg and later better known as Sir James Grigg, was a British civil servant who was unexpectedly moved, at the behest of then-Prime Minister Winston Churchill, from being the Permanent Under-Secretary of State at the War Office to become Secretary of State for War, the political head of the same department during the Second World War.

The son of Frank Alfred Grigg, a carpenter, James Grigg was born in Exmouth and won a scholarship to Bournemouth School and St John's College, Cambridge[1] where he studied mathematics, achieving first-class honours in both parts of his tripos.

He remained in New Delhi until 1939, and afterward continued to influence British imperial policies on India, especially after his patron Winston Churchill became Prime Minister.

Amongst the many Ministerial appointments made by Churchill from outside the sphere of Westminster politics, this was seen as one of the most unusual, but was a response to considerable military setbacks such as the fall of Singapore, and the need to appease critics by replacing some ministers.

Alan Brooke the wartime Army CIGS said that with PJ he had the "best and most valuable advice on any matter I discussed with him" (unlike Lawson, who replaced Grigg).