Sir Ernest Marsden (19 February 1889 - 15 December 1970) was a British-New Zealand physicist. He was born in Lancashire and educated at Queen Elizabeth's Grammar School, Blackburn, where an inter-house trophy rewarding academic excellence ('The Marsden Merit Trophy') bears his name.
He met Ernest Rutherford at the University of Manchester. While still an undergraduate he conducted the famous Geiger-Marsden experiment called the gold foil experiment in 1909 together with Hans Geiger under Rutherford's supervision. In 1915 he moved to Victoria University College, New Zealand as Professor of Physics; he was recommended by Rutherford.
Marsden served in France during World War I as a Royal Engineer in a special sound-ranging section, and earned the Military Cross. Following the war he became New Zealand's leading scientist, founding the Department of Scientific and Industrial Research (DSIR) in 1926 and organizing its research particularly in the area of agriculture. During World War II he worked on radar research, and in 1947 became scientific liaison officer in London. He died at his home in Lowry Bay, Lower Hutt on the shores of Wellington harbour in 1970.
Marsden's career recognitions included fellowship in the Royal Society of London in 1946, president of the Royal Society of New Zealand in 1947, and knighthood in 1958. The Marsden Fund for basic research in New Zealand was set up in 1994.