John C. Taylor has made significant contributions to the quantum theory of fields and the physics of elementary particles. His early important works include: the discovery (also made independently by Lev D. Landau) of singularities in the analytical structure of the Feynman integrals for processes in quantum field theory; and the discovery in 1971 of the so-called Slavnov–Taylor identities, which control symmetry and renormalisation of gauge theories.

With various collaborators, in 1980 he discovered that, unexpectedly, real and virtual infra-red divergences do not cancel in QCD as they do in QED. They also showed how these infrared divergences exponentiate. In addition, they contributed to the resummation programme in thermal QCD, simplifying the ‘hard’ part of the effective action. Recently, they studied complications arising from the non-polynomial nature of the QCD Hamiltonian in the (unitary) Coulomb gauge.