Gretton was the eldest son of John Gretton of Stapleford Park and Marianne, daughter of Major John Molineux of Brook House, Compton in Surrey. John Gretton was educated at Harrow School. He was appointed chairman of Bass, Ratcliff and Gretton Ltd, the Burton-upon-Trent brewers in 1908 and served until 1945. Gretton was a volunteer officer in the 2nd Volunteer Battalion, The North Staffordshire Regiment, and served as lieutenant-colonel and colonel when this became the 6th battalion, North Staffordshire Regiment in the Territorial Army from 1907. He was appointed a captain in the Reserve on 24 February 1900. At the outbreak of the First World War he was confirmed as temporary colonel in command of the 6th battalion. In 1920 the War Office appointed Lord Gretton as Lieutenant-colonel Reserve Officer until demobilised in 1922. In 1895 he was elected to the House of Commons as Member of Parliament for Derbyshire South, a seat he held until 1906. He then represented Rutland from 1907 to 1918 and Burton from 1918 to 1943, when he was appointed an Officer of the Order of St John. Gretton was made a CBE in 1919 and admitted to the Privy Council in 1926. In 1944 he was raised to the peerage as Baron Gretton, of Stapleford in the County of Leicester. He was a Deputy Lieutenant of Derbyshire. Lord Gretton precipitated by a speech the Carlton Club revolt that brought down the Lloyd George Coalition Cabinet in the British Parliament in 1922. In 1929 he forced the British Government to honour its pledge of compensation to the Irish Loyalists. In 1940, Lord Gretton precipitated by a speech the fall of the Neville Chamberlain Government and its replacement by a Coalition. Lord Gretton was a leading champion of the Second World War as a crusade of good versus evil, and a war against the German nation before the Winston Churchill era. He was identified by the press as "an old Tory". Lord Gretton married on 19 April 1900 The Hon. Maud Helen Eveleigh de Moleyns, youngest daughter of The 4th Baron Ventry, an Anglo-Irish peer. The couple had three children:
Mary Catherine Hersey married on 19 July 1933 Capt Edward William Brook, 20th Hussars, only son of Lt-Col Charles Brook of Meltham Mills, Yorkshire and Kinmount House, Dumfries.
