In 1815, the Swedish chemist J. J. Berzelius obtained a material which he regarded as a new earth. He assigned this to a new oxide and the corresponding metal name was intended to honor Thor, the ancient Scandinavian god of thunder. However, in 1824, he demonstrated that this supposedly new earth was essentially the phosphate of previously discovered yttrium. Four years later, the Reverend H. M. T. Esmark discovered a black mineral on the island of Lovo near Brevig, Norway; he gave a sample of this material to his father, Professor Jens Esmark, a noted mineralogist. Professor Esmark was unable to identify it as any known mineral, so he in turn sent a specimen to Berzelius for examination. A chemical analysis of this mineral by Berzelius demonstrated that it contained almost 60% of a new earth which he reported as distinct from all others known. It appears that, in naming this new oxide "thoria" and the mineral which it was obtained "thorite", Berzelius fully restores the dignity of Thor from the earlier near humiliation. The discovery of thorium was announced by Berzelius in a publication in 1829. He also prepared thorium in metallic form in that year by heating a mixture of potassium metal with potassium thorium fluoride in a glass tube. The metal appeared as a gray powder since the reduction reaction was not sufficiently exothermic to melt the thorium metal product.

Thorium and its compounds were used only for academic purposes until 1884, when Auer von Welsbach developed and patented the incandescent gas light mantle in which thorium oxide was the essential ingredient. The mantle industry grew to its peak in the early of the 20th century, but as electricity began to replace gas for general lighting purposes, mantle production decreased and by 1925 thorium was relatively unimportant to commerce. With the advent of atomic energy, thorium jumped back to an important role in nuclear power plants due to its nuclear properties.