He was one of the founders of the Comité de vigilance des intellectuels antifascistes, an anti-fascist organization created after the 6 February 1934 far right riots.

Langevin is noted for his work on paramagnetism and diamagnetism, and devised the modern interpretation of this phenomenon in terms of spins of electrons within atoms.

During his career, Paul Langevin also spread the theory of relativity in academic circles in France and created what is now called the twin paradox.

In 1910, he reportedly had an affair with the then-widowed Marie Curie;[9][10][11][12] some decades later, their respective grandchildren, grandson Michel Langevin and granddaughter Hélène Langevin-Joliot married one another.

The amount of time taken by the signal to travel to the enemy submarine and echo back to the ship on which the device was mounted was used to calculate the distance under water.

In 1916, Lord Ernest Rutherford, working in the UK with his former McGill University PhD student Robert William Boyle, revealed that they were developing a quartz piezoelectric detector for submarine detection.