Niels Johan Føyn, original surname Nielsen (February 23, 1860 – June 13, 1945) was a Norwegian meteorologist.

Føyn was born in Slagen in the municipality of Tønsberg, Norway.

[1][2] He was the son of the ship operator Peder Nielsen (1818–1904) and he later adopted the surname Føyn from the oeconym of the farm where his family lived.

[2] He received his candidatus realium degree in 1886 and then worked as an assistant at the Norwegian Meteorological Institute.

[1] He was made a member of the Norwegian Academy of Science and Letters in 1904.