His key achievements include calculating relativistic effects on the spin-orbit interaction in a hydrogenic atom (Thomas precession), creating an approximate theory of

Born in London, he studied at Cambridge University, receiving his BA, PhD, and MA degrees in 1924, 1927 and 1928 respectively.

While on a Traveling Fellowship for the academic year 1925–1926 at Bohr's Institute in Copenhagen, he proposed Thomas precession in 1926, to explain the difference between predictions made by spin-orbit coupling theory and experimental observations.

The Thomas collapse is effect in few-body physics, which corresponds to infinite value of the three body binding energy for zero-range potentials.

In mathematics, his name is frequently attached to an efficient Gaussian elimination method for tridiagonal matrices—the Thomas algorithm.