As a scientist, he carried out research into star formation and plasma physics and in 1946 conceived the idea of telescopes operating in outer space.

During a year of study at St John's College, Cambridge, he was influenced by Arthur Eddington and the young Subrahmanyan Chandrasekhar.

Returning to the U.S., Spitzer received his Ph.D. in physics from Princeton University in 1938 after completing a doctoral dissertation, titled "The spectra of late supergiant stars", under the direction of Henry Norris Russell.

[7][8][9] In 1965, Spitzer and Donald Morton became the first to climb Mount Thor 1,675 m (5,495 ft), located in Auyuittuq National Park, on Baffin Island, Nunavut, Canada.

In 1947, at the age of 33, he succeeded Russell as director of Princeton University Observatory, an institution that, virtually jointly with his contemporary and friend Martin Schwarzschild, he continued to head until 1979.