Marmet is notable for developing a novel high-resolution electron velocity selector, a scientific instrument which became widely used by scientists around the world.

[6] Along with a mass spectrometer Marmet developed, the novel instrument had an energy resolution superior to then-available instruments and has been used widely by scientists studying electron scattering, which led to the discovery of enhanced vibrational excitation in nitrogen and of Feshbach resonances.

The group also found negative-ion resonances in which the incident electron temporarily attaches to the target molecule.

In his later years, Marmet became an outspoken critic of the Copenhagen Interpretation of quantum mechanics, the theory of relativity, and the Big Bang cosmological model.

[13] Marmet was one of 34 signers of An Open Letter to the Scientific Community advocating against the Big Bang cosmology.