He moved to the United States of America in 1964, where he lived the rest of his life, though he retained British citizenship.

[14] He made major contributions to the theory of approximate molecular orbital (MO) calculations, starting with one identical to the one developed by Rudolph Pariser and Robert G. Parr on pi electron systems, and now called the Pariser–Parr–Pople method.

While in the early days these calculations were extremely expensive to perform, the advent of high speed microprocessors has made them much more feasible today.

[17] One of his most important original contributions is the concept of a model chemistry whereby a method is rigorously evaluated across a range of molecules.

In 1991, Pople stopped working on Gaussian and several years later he developed (with others) the Q-Chem computational chemistry program.

[19] Prof. Pople's departure from Gaussian, along with the subsequent banning of many prominent scientists, including himself, from using the software gave rise to considerable controversy among the quantum chemistry community.

[23] In accordance with his wishes, Pople's Nobel Medal was given to Carnegie Mellon University by his family on 5 October 2009.