Lycodes esmarkii was first formally described by the Norwegian zoologist Robert Collett with the type locality given as Varanger Fjord in northern Norway.

This is a long-tailed eelpout, with the distance from the snout to the origin of the anal fin being equivalent of 36% to 44% of the total length.

This is a large species and has benn recorded as attaining a total length of 102 cm (40 in) off Iceland.

The greater eelpout is a bathdemersal species which occurs at depths between 143 and 1,090 m (469 and 3,576 ft) where the temperature varies between −0.6 and 5.6 °C (30.9 and 42.1 °F).

They may reach an age of 12 years, based on otoliths sampled from a specimen with a total length of 63 cm (25 in) taken in the Barents Sea.