He was born in Bergen as a son of shipmaster and merchant Mads Christensen Nygaard (1793–1875) and Maren Behrens (1806–1875).
In 1887 he published the Latin-Norwegian dictionary Latinsk Ordbog together with Jan Johanssen and Emil Schreiner, a book which is still in use—it has been updated and reissued, last in 1998.
[3][4] He published Kortfattet Fremstilling af det norske Landsmaals Grammatik in 1867, a very early grammar of Landsmål.
Together with Jonathan Aars he was also a driving force behind the Norwegian orthographic reform of 1907, which marked a split between Dano-Norwegian and the new Riksmål.
[1] He was decorated with the Royal Norwegian Order of St. Olav in 1890, and died in February 1912 in Kristiania.