Roy's work in Kaon physics during his doctoral studies at Stanford University was based on the applications of algebra in the discipline and his thesis was subsequently published by the university under the title, Current-algebra Applications in Kaon Physics. Later, he worked on scale invariance and deep inelastic scattering while at CERN, Geneva and his research thereafter has covered several aspects of high energy physics. Roy has developed a new sum rule in two-photon processes which is related to the collision of two real polarised photons and the equation is now known as Roy's Sum Rule. Further, he proposed a solution for U(n)-symmetric Thirring model which has been detailed in two of his articles published in 1975. Later, shifting his focus to supersymmetry and supergravity, he suggested new τ -number violating signals for R-parity breaking and estimated an upper bound on the gaugino-gravitino mass ratio. Deep inelastic lepton - hadron - photon processes with regard to their phenomenological aspects have been another area of his studies. Roy has also done extensive studies on neutrinos and Higgs mesons which covered the detection of heavy neutrinos, ultralight neutrinos in super-symmetry, oscillations and flavours, and his studies on neutrino detection helped India-based Neutrino Observatory in blueprinting the proposed detector at the observatory.