John Trevor Lewis (15 April 1932 – 21 January 2004) was a Welsh mathematical physicist who made contributions to areas including quantum measurement, Bose–Einstein condensation and large deviations theory.

[1] He was a senior professor at the Dublin Institute for Advanced Studies (DIAS) in Ireland from 1972, serving as the director of the School of Theoretical Physics from 1975 until his retirement in 2001.

Lewis was born in Swansea, Wales, and was educated at Cardiff High School and then the Royal Belfast Academical Institution.

[2] He then studied at Queen's University Belfast, earning BSc in 1952 and PhD in 1955, the latter for a thesis on "Quantal Calculations Relating to Certain Rate Processes" done with Alexander Dalgarno and David Bates.

[4] In 1972, he moved to the Dublin Institute for Advanced Studies on the retirement of John L. Synge,[1] where he served as director of the School of Theoretical Physics.