[6] O. tetricus is distributed in the subtropical seas of eastern Australia and northern New Zealand, including Lord Howe Island.

A close relative, Octopus djinda, occurs at similar latitudes in Western Australia, from Shark Bay to Cape Le Grand,[7] and was considered to be conspecific with O. tetricus until 2021.The first sighting of O. tetricus in New Zealand wasn't until 1997,[4] and has since become one of the most common species of octopus found in New Zealand, alongside Pinnoctopus cordiformis and Macroctopus maorum.

[9] O. tetricus populations in New Zealand are found along the North-East coast of the North Island, between the Bay of Plenty and Northland.

It is proposed that the mechanism for gene flow across the Tasman Sea is through planktonic larve and/or adults using floating wood or algae as transport.

Octopus tetricus is normally coloured grey to mottled brown with rufous arm faces that taper towards the tip.

The skin is granular, and has many small irregularly shaped patches and large warty structures used to make it appear spiky when the octopus camouflages itself as seaweed.

Females reach maturity around Australia's spring and summer seasons in order to mate and lay eggs.

The amount of time embryonic development takes varies with water temperature, and newly hatched O. tetricus larvae are about 2.5 mm long and 1.1mm wide,[24] approximately the size of a grain of rice.

With a good food supply, octopuses that reside in areas with a cooler water temperature tend to grow slower during the key growth phase and when they reach maturity they are generally larger than octopuses that are found in warmer water temperatures.

[8] Adult O. tetricus is observed to have a relatively small body size and a lifespan of approximately 11 months,[21] although there is evidence that they can live up to 2 years.

[8] Female O. tetricus rarely eat or sleep during the protection of the nest, devoting all resources to nourishing its offspring, and die shortly after the eggs hatch.

They tend to have a preference for materials that are free from barnacles and encrustations, although the scale on which this is the case is dependent on foraging success.

[13] This species can be found across a variety of coastal environments all year round, but there are some observations of adults aggregating inshore for breeding purposes during spring and summer.

[25] The likelihood of an aggressive encounter leading to a physical altercation is increased when there is a significance difference in the relative darkness of body patterning between the two individuals.

[11] In general, the species will avoid aggressive encounters, as they have a high cost to reward ratio and can also result in physical damage to their body.

Female octopuses are able to accept multiple spermatophores from males but they only produce one brood of eggs at the end of a mating season.

[25] Octopus tetricus is primarily a nocturnal feeder which uses its sharp beak to feed on crustaceans and molluscs, for example sea snails and bivalves.

O. tetricus predation influences hermit and lobster densities and habitat choice, modifying ecosystem dyanmics and trophic interactions of various species.

[31][32] Animals that predate on O. tetricus include some species of dolphin, the short-tail stingray (Dasyatis brevicaudata), southern eagle rays (Myliobatis goodei), wobbegong sharks, and some fish.

Generally, O. tetricus are considered a solitary, crespular species, meaning they emerge from their dens to hunt and feed alone at dusk and dawn before returning to the safety of their enclosures to consume prey and to spend their daytime.

[11][26] High density aggregations of the species is most common when there is limited den opportunities and plentiful food abundance.

O. tetricus regulate energy flux between trophic levels within the marine ecosystem by mediating the amount of prey that can be consumed by other octopus species.

Octopus rely majorly on visual cues when detecting predators and prey, using polarised light.

[27] O. tetricus display episodic personality, meaning that they alter and change their behaviour based on the environment and circumstances of the octopus at the time.

[34] Differences in behaviour between sexes of the species are apparent, such as males being less likely to modify dens and shelters compared to females.

[10] The ability of O. tetricus to quickly modify the pattern, colour, and texture of their skin is a tool for signalling to other octopus, as well as crypsis which is used for both anti-predator and predation strategies.

[36] Changes in skin properties can be used to signal that they feel threatened, for example when faced with a predator, or when a female rejects a males advances for mating.

Octopus tetricus may be caught as bycatch in trawl and lobster-pot fisheries and is then sold for both human consumption and for use as bait.

[3] The species made up to 43% of total cephalopod fishing catches in 2007, however, it is possible that O. tetricus was sometimes misidentified as Octopus australis.