Niels Janniksen Bjerrum, born March 11, 1879 in Copenhagen, died September 30, 1958, was a Danish chemist.

Niels Bjerrum was the son of opthamologist Jannik Petersen Bjerrum, and started to study at University of Copenhagen in 1897. He received his Master's degree in 1902 and his Doctor's degree in 1908, and did research in coordination complex chemistry under Sophus Mads Jørgensen. He became a docent in 1912, and in 1914 he became professor of chemistry at the Royal Agricultural College (Landbohøjskolen) in Copenhagen, as successor of Odin Tidemand Christensen. He stayed on this post until his retirement in 1949, and from 1939 to 1946 he was also the Director of the College.

He is noted for the theory behind the Bjerrum length.

His son Jannik Bjerrum (1909 – 1992) became also a chemist and was active in the area of complex chemistry.