Roger Thomas is internationally recognised for his pioneering work on the development of ion-sensitive microelectrodes. He invented the recessed tip electrode, allowing tip diameters of less than 1 micrometre and so permitting the use of these electrodes in a wider range of cells.

He has used these microelectrode techniques to characterise the electrogenic sodium pump in neurons and has become an authority on intracellular pH and calcium regulation in large snail nerve cells. His methods have now largely been superseded by optical techniques and fluorescent indicators. His own experiments involve recording many variables simultaneously from single cells.