Niels Thomsen was born in 1945 and studied in Copenhagen, Philadelphia, Italy, England and USA. From 1967 he was solo clarinettist in various Danish provincial orchestras, and in 1976 he was appointed solo clarinettist in The Danish National Symphony Orchestra, where he remained until he retired in 2008.
Niels Thomsen appeared frequently as a soloist with his own and other Danish orchestras, and appeared abroad as a soloist in Germany, Russia, the Czech Republic, and France. He was also a member of the Danish chamber orchestra Collegium Musicum.
Niels Thomsen's solo recordings include concertos by Carl Nielsen, Poul Ruders, and Weber and his chamber music recordings include Carl Nielsen's Wind Quintet with James Galway and the clarinet sonatas of Brahms with Elisabeth Westenholz. His awards include the Jacob Gade Prize and the distinguished artist's award of the Carl Nielsen and Anne Marie Carl-Nielsen Fund.