Alexander was born in London to aristocratic parents and was educated at Harrow before moving on to the Royal Military College, Sandhurst, for training as an army officer of the Irish Guards. He rose to prominence through his service in the First World War, receiving numerous honours and decorations, and continued his military career through various British campaigns across Europe and Asia. In the Second World War, Alexander oversaw the final stages of the Allied evacuation from Dunkirk and subsequently held high-ranking field commands in Burma, North Africa and Italy, including serving as Commander-in-Chief Middle East and commanding the 18th Army Group in Tunisia. He then commanded the 15th Army Group for the capture of Sicily and again in Italy before receiving his field marshal's baton and being made Supreme Allied Commander Mediterranean.