Geologist. Born in Yorkshire, Harker was educated in Hull, Windsor and St. John's College, Cambridge. He remained in Cambridge as a lecturer in geology. In 1895, Archibald Geikie asked Harker to work part-time for the Geological Survey of Great Britain to assist with the mapping of Skye and the Small Isles. Harker is credited with first recognising the rock Mugearite and naming it after Mugeary on Skye. He became a member of the Scottish Mountaineering Club.
He was an early pioneer of the use of thin sections to investigate rocks, and his publications include The Tertiary Igneous Rocks of Skye (1904) and The Natural History of Igneous Rocks (1909). He was regarded as the premier British petrologist of the early 20th C., although his theory of broad geological provinces has subsequently been discounted. Harker was awarded the Geological Society's Murchison Medal (1907), served as their President (1916-18) and was awarded their Wollaston Medal (1922).
He died in Cambridge. The Harker Geological Collection at the Sedgwick Museum there is named after him and comprises more than 150,000 specimens.