Although the bluntnose sixgill shark is found from the surface to depths of 2500 m, it is primarily a deepwater species found in waters below 91 m. The species is mostly found over the outer continental and insular shelves. Young bluntnose sixgill sharks are thought to remain in shallower waters of the continental shelf and uppermost slope until they reach adolescence, at which time they move further down the slope and into deeper water. In Canada's Pacific waters immature bluntnose sixgill sharks regularly make forays into shallow waters in some locales allowing the opportunity for scuba divers to observe them.

The bluntnose sixgill shark, with a maximum reported length 4.8 m, is the largest predatory shark regularly encountered in Canada's Pacific waters. The name, sixgill, refers to the presence of six gill slits whereas most other shark species have only five. It is easily distinguished from other sharks as it has only a single dorsal fin, compared to two in all other shark species normally found on Canada's Pacific coast. Its colour is a dark brown or grey to black on their back dorsal side with the colour becoming lighter towards their underside. Its head is broad and depressed with a blunt snout and its eyes are bright green. With this species females grow larger than males. Length at maturity has been reported for females to be 421-482 cm. For males length at maturity is 310 cm. Age of maturity is widely reported at 11-14 years for males and 18-35 years for females as is an estimated longevity of up to 80 years, but these values have not been confirmed through valid aging studies.