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. 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.He also founded the Communications Networks Research Institute at Dublin Institute of Technology.