Johan Hjort had wanted to become a zoologist since his early schooldays, but to please his father he took initial courses in medicine, before following Fridtjof Nansen's advice and his own wish, leaving for the University of Munich to study zoology with Richard Hertwig.

He returned to Norway to become curator of the University Zoological Museum, where he developed more modern courses for students, and in 1894 he succeeded G. O. Sars as Research Fellow in Fisheries.

He was the first to apply actuarial statistical methods to study these phenomena, aided also by measurement techniques that made it possible to estimate the age of sampled fish.

Around 1898, Hjort adapted earlier designs of deep-sea trawls on the soft bottoms of the deep Norwegian fjords and soon discovered enormous stocks of Pandalus borealis.

[2] Many years later, when travelling to Harvard in 1936 to collect an honorary degree, he predicted that the deep-sea shrimp would be found off the New England coast, since the ecological conditions were similar to those of the soft-bottomed Norwegian fjords.

Hjort was a frequent contributor to public debate, and wrote books, essays and newspaper articles on themes ranging from popularisation (and unification) of science to politics and philosophy.

For his achievements in science and in practical oceanographic and fisheries research Hjort was awarded several honours, including honorary degrees from the universities of Cambridge, Harvard and London.

Sir Alister Hardy writes the following about Hjort: "He was one of the great leaders in oceanography whose names will live in the annals of that science [...] His fame will last both for the contributions he made to oceanic biology, especially in that classic The Depths of the Ocean which he published with Sir John Murray as a result of their North Atlantic expedition in 1910, and equally for his remarkable pioneer achievements in practical fisheries research.

In his book about Norwegian scientists, Francis Bull gave the following description of Hjort: "As a superior, he was without peer; helpful, kind, patient – as an equal, rather difficult, because he always believed he was right – and as a subordinate, sure of himself and full of the desire to oppose.