Birkeland was born in the Norwegian capital, Christiania (now Oslo), and studied in Paris, Geneva, and Bonn where he was a pupil of Robert Bunsen. In 1898 he was appointed to the chair of physics in Oslo University. He is remembered today for his discovery of a means for the fixation of nitrogen (the Birkeland–Eyde process).

In 1898 William Crookes in his presidential address to the British Association had pointed out that, given the world demand for nitrogeneous fertilizers, the deposits of nitrates would rapidly be exhausted. As there is a virtually unlimited supply of nitrogen in the atmosphere the obvious solution was to find some way in which it could be used. Birkeland, in collaboration with Samuel Eyde, solved the problem in 1903 by passing air through an electric arc to form oxides of nitrogen, which could then be absorbed in water to give nitric acid. This was mixed with lime to give calcium nitrate. The process is particularly useful in regions (as in Scandinavia) where there is a plentiful supply of hydroelectric power, although the Haber process is now the main industrial method of fixing nitrogen.

Birkeland also spent much time studying the aurora borealis, making several expeditions and establishing a geophysical laboratory as far north as 70°. In 1896 he was the first to suggest the correct explanation that the aurora borealis could be the result of charged rays emitted by the Sun and trapped in the Earth's magnetic field near the poles. He derived this idea from the resemblance between the newly discovered cathode rays and the aurora.