He successfully deciphered the Turkic Orkhon inscriptions which were discovered during the expedition of Nikolai Yadrintsev in 1889.

[2] He studied at the University of Copenhagen in 1859, graduating in 1867 and earning a PhD in 1869 with a dissertation on Germanic loanwords in Finnic.

[3] In 1876 he was invited to give the Ilchester Lectures at the University of Oxford, which were later published as The Relations Between Ancient Russia and Scandinavia, and the Origin of the Russian State.

[4] Thomsen made a number of important contributions to linguistics, including his work on the Germanic, Baltic, and Indo-Iranian influences on Finnic.

[5] In 1893, he deciphered the Turkic Orkhon inscriptions ahead of Russian linguist Wilhelm Radloff (1837–1918).