Trenchard was born in Taunton, England on February 3, 1873. At the age of twenty, he enlisted in the British Army in 1893 serving in Africa. In 1913 he was transferred to the Royal Flying Corps (RFC) as second in command of the Central Flying School. In August 1915, Major-General Trenchard became the RFC's General Officer Commander in the field.
In August 1917 he agreed to return to Britain and re-organise training with Robert Smith-Barry at a new school at Gosport. The curriculum combined classroom training and dual flight instruction. Students were not led away from potentially dangerous manoeuvres but deliberately exposed to them in controlled environments so they could learn to recover from errors of judgement.
The Air Council was formed in January 1918, and Trenchard became Chief of the Air Staff. He helped establish the RAF in April 1918, but resigned two weeks before its inauguration after a quarrel with the Air Secretary, Lord Rothermere.
Returning to active duty, Major-General Trenchard began in June 1918 to organize intensive strategic bombing attacks on German railways, airfields and industrial centres. These attacks used the RAF's 55 & 100 squadrons as part of the Independent Air Force based near Nancy, France, and continued until the end of the war.
Trenchard returned as Chief of the Air Staff in 1919 under Winston Churchill, and remained until retiring in 1929.
On 17th July 1920, Air Marshal Sir Hugh Trenchard married Katherine Boyle, the widow of James Boyle, son of the Earl of Glasgow, at St. Margaret's Church in Westminster.
After the war, the RAF was budgeted to shrink from over 250 to 25 squadrons. Against this background of demobilisation and continued savage budget cuts, Trenchard fought to keep the air force separate from army and navy, and built the basis for a much larger organisation whose time would come in 1940.
Trenchard showed the effectiveness of strategic bombing for colonial counter-insurgency by 1920's operations in Somaliland and Iraq. He wrote that the RAF could even suppress “industrial disturbances or risings” in England itself. Churchill told him not to refer to this proposal again, but by World War II strategic bombing had become standard military doctrine.
In 1930 he entered the House of Lords as The Viscount Trenchard of Wolfeton, and was appointed commissioner of the Metropolitan Police. Trenchard carried important police reforms and established the Police College at Hendon.
He died on February 10, 1956.