In the years prior to the description of this species in 1953, O. rubescens was widely considered to be a young Enteroctopus dofleini. Many early descriptions were based on a combination of O. rubescens and E. dofleini. To date, the taxonomy of this species remains somewhat unresolved. S.S. Berry’s 1953 description is in truth a brief diagnosis, and considering the exceptionally wide range of the species, the animals currently covered under O. rubescens may prove to represent several subspecies or a species complex.
O. rubescens generally grows to a mantle length of 8–10 cm, and arm length of 30–40 cm. Adult weight is generally 100–150 grams, but animals up to 400 grams in weight have occasionally been observed.
Like all octopuses, O. rubescens can change its color and texture, making its appearance highly variable. Color can vary from a deep brick red, to brown, to white, or mottled mixtures of the three. It can be easily confused with small individuals of Enteroctopus dofleini in the northern end of this species' range. The two can be differentiated by the presence of three eyelash-like papillae below the eyes of O. rubescens that are absent in E. dofleini.Like most octopuses, O. rubescens is thought to be among to the most intelligent of invertebrates. The presence of individual personalities is a hallmark of intelligence, and O. rubescens was the first invertebrate in which individual personalities were demonstrated.
O. rubescens is a generalist predator and has been maintained on a wide variety of gastropods, bivalves, crabs and barnacles in the lab. So far, very little quantification of its diet in the wild has been made. The two studies on the subject determined diets in Puget Sound, Washingtonto be dominated by gastropods, particularly Nucella lamellosa and Olivella baetica, but also composed of clams, scallops and crabs. Theplanktonic larvae of O. rubescens have also been observed in the wild to consume krill. 
As part of its feeding behavior, O. rubescens will pounce on prey and display a stereotypical sequence of color changes at the moment of capture. Following the capture of bivalve prey, it will often drill a hole through the shell to deliver venom and more easily open the shell. The octopuses will often concentrate their drill holes near the adductor muscles of the bivalve prey.
A recent study has suggested O. rubescens may choose prey based on fat digestibility rather than on the amount of calories the octopus is able to obtain from the food items.  If this is true, the authors further argue, this would make O. rubescens a specialist predator by some measures, rather than a generalist, due to it specific nutrient requirements.