Later, in 1913, he became the government entomologist at the Norwegian Plant Protection Office (Statens plantevern), a position that he held for 42 years.

[1][dubious – discuss] Thor Hiorth Schøyen became interested in nature and insects at an early age, and he studied zoology at the University of Oslo.

Following in his father's footsteps, in 1913 Thor Hiorth Schøyen assumed the position of Norway's government entomologist.

[6] Schøyen worked in an office with no assistants, and he responded to hundreds of pest and fungal disease requests annually.

[1] Thor Hiorth Schøyen authored a number of publications, many of which were popular science articles about pests in agriculture and forestry.

These contained much information about insects in Norway, including discoveries of new species and interesting biological observations.