The Pacific staghorn sculpin was first formally described in 1854 by the French biologist Charles Frédéric Girard with its type locality given as San Francisco in California.

[2] The 5th edition of Fishes of the World classifies the genus Leptocottus within the subfamily Cottinae of the family Cottidae,[3] The Pacific staghorn sculpin's genus name, Leptocottus, is a combination of leptos, meaning "slender", and Cottus.

The specific name armatus means "armed", a reference to the large and sharp spines on the preoperculum.

[4] Pacific staghorn sculpins are slender fish,[4] with a wide, large, highly flattened head with a body which tapers towards the tail.

[6] The Pacific staghorn sculpin is found in the eastern Pacific Ocean along the western coast of North America from the Izembek Lagoon, on the southeastern Bering Sea coast of Alaska[6] south as far as San Quintín, Baja California.

The larval stage starts in estuarine environments, being found over soft and sandy substrates.

[7] Each female lays between 2 and 10 thousand eggs and following spawning adults rapidly leave for deeper waters.