D'Urban was born in Halesworth, the youngest but only surviving son of Benjamin D'Urban, and joined the British Army in 1793, enlisting as a cornet in the Queen's Bays at the age of sixteen. He made rapid progress in the Army and distinguished himself in the Peninsular War. Assigned to the Portuguese army, he was quartermaster general and chief-of-staff to William Carr Beresford, 1st Viscount Beresford. He served in all the principal sieges and battles, never asked to go on leave, and was laden with honours, being appointed Knight Grand Cross of the Order of the Bath, Knight Commander of the Royal Guelphic Order, and Commander of the Portuguese Order of the Tower and Sword. He received the Army Gold Cross and five clasps for the battles of Busaco, Albuera, Badajoz, Salamanca, Vitoria, the Pyrenees, Nivelle, the Nive, and Toulouse.