Harington's military career began on 12 June 1852, when he was commissioned as a 2nd Lieutenant in the Bengal Artillery. During the Indian Mutiny he was severely wounded at Trimmoo Ghat. He was present throughout the Siege of Delhi, and after the fall of the city he proceeded with the Grethed's column towards Cawnpore taking an active part in the engagements at Maligurh Fort, Allygurh and Agra. He was present at the relief of the garrison at Lucknow, where his courage gained him the Victoria Cross, for which he was elected by the vote of his fellow officers. During these operations he was most dangerously wounded.