Scottish soldier and explorer who accompanied John Hanning Speke (Speke, John Hanning) in the search for and discovery of the source of the Nile River.

Commissioned in the British army in 1846, Grant saw action in India in the Sikh Wars and the Indian Mutiny of 1857. When Speke started his second African expedition in 1860, he asked Grant, his friend and comrade in India, to join him. A loyal lieutenant, Grant for long intervals during the expedition was given independent command of part of the caravan. After great hardship, they found the outlet of Lake Victoria from which the Nile issued (July 1862). For his services, Grant was awarded a gold medal by the Royal Geographical Society. During the 2 ¹/₂-year journey, Grant had kept a journal describing events of geographic significance and the customs of native peoples; it was published under the title A Walk Across Africa (1864). In 1868 Grant served in the intelligence department under Lord Napier during the Ethiopian campaign, retiring from the service that same year with the rank of lieutenant colonel.