He was born in Edinburgh, the son of James Stuart Geikie and younger brother of Sir Archibald Geikie. He was educated at the Royal High School, Edinburgh and University of Edinburgh.
He served on the Geological Survey from 1862 until 1882, when be succeeded his brother as Murchison professor of geology and mineralogy at the University of Edinburgh. He took as his special subject of investigation the origin of surface-features, and the part played in their formation by glacial action. His views are embodied in his chief work, The Great Ice Age and its Relation to the Antiquity of Man (1874; 3rd ed., 1894).