McClelland was the son of William McClelland of Dunallis,
Coleraine and received his education at
Queen's College, Galway. In 1895 he received a fellowship from the
Royal University of Ireland and spent 1896–1900 at
Cavendish Laboratory, while pursuing a research degree at
Cambridge. In 1900 he was appointed Professor of Experimental Physics at
University College, Dublin. and in 1917 was awarded the Boyle medal of the
Royal Dublin Society. In 1901 married Ina Esdale. They had five children. John A. McClelland died on 13 April 1920. ==References==