John Alexander McClelland FRS (1 December 1870 – 13 April 1920) was an Irish physicist known for pioneering work on the scattering of β rays, the conductivity of gases, and the mobility of ions.
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.