He studied in Copenhagen from 1740, at Halle in Germany from 1742, and at Jena from 1744, where he received his Magister degree in 1745 and in 1753 was admitted to the Faculty of Philosophy.

[1] Gunnerus was very interested in natural history and accumulated a large collection of specimens from visits to central and northern Norway.

In 1765 Gunnerus published a description of a basking shark in this journal, giving it the scientific name Squalus maximius.

He contributed notes on the ornithology of northern Norway to Knud Leem's Beskrivelse over Finmarkens Lapper (1767), translated into English in 1808 as An Account of the Laplanders of Finmark.

[2] Gunnerus was the first to suggest that since the northern lights were caused by the Sun, there also had to be auroras around the moon, Venus and Mercury.