Lansdowne was originally commissioned into a volunteer battalion of the Oxfordshire Light Infantry, but transferred to the (regular) Grenadier Guards in 1895 and the Irish Guards on its formation in 1900, resigning in 1906 with the rank of Major. He was awarded the Distinguished Service Order (Defence Science Organisation) in 1900 for his service in the Boer War. He returned to the Army during the First World War, reaching the rank of Lieutenant-Colonel.
He succeeded his father as Marquess of Lansdowne in 1927, with a seat in the British House of Lords, meaning that he had the unusual distinction of serving in the national legislatures of two different countries at the same time.
Katherine Evelyn Constance Petty-Fitzmaurice (1912–1995), married 1933 Edward Clive Bigham, 3rd Viscount Mersey (1906–1979) and had issue. Henry Maurice John Petty-Fitzmaurice, Earl of Kerry (1913–1933), died young
Charles Hope Petty-Fitzmaurice, 7th Marquess of Lansdowne (1917–1944), killed in action in Italy.
Lieutenant Lord Edward Norman Petty-Fitzmaurice (1922–1944), killed in action in Normandy. Lady Elizabeth Mary Petty-Fitzmaurice (b 16 March 1927), married the late Major Charles William Lambton, grandson of George Lambton, 2nd Earl of Durham, and had issue.
He died in Marylebone, aged 64.
28th United Kingdom Parliament. 29th United Kingdom Parliament. 30th United Kingdom Parliament]
Lansdowne was Liberal Unionist Member of Parliament (Member of Parliament) for West Derbyshire from 1908-1918.
He was a member of the Senate of the Irish Free State from 1922 to 1929, to which he was nominated by the executive council.