Henry David Reginald Margesson was born in 1890, the son of Sir Mortimer Margesson. He was educated at Harrow and Magdalene College, Cambridge. During the First World War, Margesson served as an Adjutant with the 11th Hussars, for which he was awarded the Military Cross. In 1916, he married Frances Legett, with whom he had 1 son and 2 daughters. The marriage ended in divorce in 1940.

From 1922-3 Margesson was the Unionist (Conservative) candidate for West Ham then for Rugby (1924-42). In 1931, he became Parliamentary Secretary to the Treasury. Margesson served in the Conservative Chief Whips' Office for about 14 years and was Government Chief Whip from 1931-40, serving 4 Prime Ministers, Ramsay MacDonald, Stanley Baldwin, Neville Chamberlain and Winston Churchill. As Chief Whip, Margesson sought to maintain government support through the debates on the Government of India Bill (opposition to which was led by Winston Churchill) and throughout Chamberlain's appeasement policy leading up to Word War II. From 1940-42, Margesson served as Secretary of State for War, after which he was made 1st Viscount Margesson of Rugby. He died on 24 December 1965.