Promethium was the last of the rare-earths family elements to be discovered in Nature. It was only in 1965, and after innumerous attempts to isolate the metal from natural ores, that O. Erametsa was able to obtain about 20 tons of rare-earths starting from 6000 tons of apatite. From these, he isolated a small fraction of 350 milligrams of a radioactive element which he thought to be the isotope 147 of the element with atomic number 61. However, the discovery of the element is attributed to J. A. Marinsky and L. E. Glendenin, that, in 1945, identified the 147-Pm in the by-products uranium fission.

The element was isolated three years later in Oak Ridge Laboratory (USA) by G. W. Parker and P. M. Lantz. The metal was prepared for the first time by F. Weigel in the University of Munich, in 1963.