Hugh Trenchard was born on 3 February 1873, the second son of Henry Montague Trenchard, solicitor, and his wife, Georgina.

Trenchard entered the army in September 1893, as second lieutenant in the 2nd battalion, Royal Scots Fusiliers, first serving in India, then on the outbreak of the Second Boer War in October 1899, being sent to South Africa. Promoted to captain in February 1900, he was severely wounded, and invalided home to England in December, but insisted on returning to South Africa in May 1901. While on leave at the end of the war Trenchard was made assistant commandant of the South Nigeria regiment in October 1903, first as major, then as lieutenant-colonel. In 1908 he was appointed to command his regiment, but was again invalided home in 1910. On recovering, he rejoined the Royal Scots, dropped in rank to major, and served in Ulster until 1912.

In 1912, looking for a new challenge, Trenchard decided to learn to fly. After only two weeks of tuition, he qualified as a pilot on 31 July. The Royal Flying Corps having been formed in May of that year, Trenchard was sent to the RFC's Central Flying School at Upavon in Wiltshire. In spite of having only just qualified, he was appointed to the staff as assistant commandant.

On the outbreak of war in August 1914 Trenchard took command of Farnborough, Hampshire. A few months later in November, he was on the western front as an operational commander. From 1915 Trenchard pressed hard for more powerful aircraft, and particularly for more aggression among pilots. In August 1915 Trenchard succeeded Sir David Henderson as head of the Royal Flying Corps in France and was promoted to brigadier-general. Reluctantly, Trenchard became Chief of the Air Staff in January 1918, but resigned a few months later in April as a result of a campaign led by the Air Minister, 1st Lord Rothermere, against his hero General Sir Douglas Haig. Trenchard then returned to France later that month as head of a small force of bombers.

Trenchard was created a baronet in October 1919 and resumed his post as Chief of the Air Staff in May 1920. Trenchard was knighted again (GCB) in January 1924 and became the first Marshal of the RAF in 1927. He retired on 31 December 1929 and was made a baron next day. Although Winston Churchill offered him command of Britain's home forces and also a role in military intelligence during the Second World War, Trenchard refused both posts, but was tireless in promoting his belief in the bomber as the mainstay of air power.

In July 1920 Trenchard had married Katherine Isabel Salvin (d. 1959), having two sons. He died on 10 February 1956.