The type and only species, S. inequalis, was named by Charles Mortram Sternberg in 1932, based on a foot, fragments of a hand, and some caudal vertebrae from the Late Cretaceous of Alberta.

A couple of cranial specimens were also referred to the genus: UALVP 52611 (a nearly complete skull roof) and TMP 1986.036.0457 (a partial braincase).

He reclassified Stenonychosaurus inequalis as well as Polyodontosaurus grandis and Pectinodon bakkeri as junior synonyms of Troodon formosus.

[4] In 2011, Zanno and colleagues reviewed the convoluted history of troodontid classification in Late Cretaceous North America.

[5] In 2017, Evans and colleagues, building on the work of Zanno and others, confirmed the currently undiagnostic nature of the holotype of Troodon formosus and suggested that Stenonychosaurus be used for troodontid skeletal material from the Dinosaur Park Formation.

In 1982, Dale A. Russell, then curator of vertebrate fossils at the National Museum of Canada in Ottawa, conjectured a possible evolutionary path for Stenonychosaurus, if it had not perished in the Cretaceous–Paleogene extinction event, suggesting that it could have evolved into intelligent beings similar in body plan to humans.

Russell had discovered the first Troodontid skull, and noted that, while its EQ was low compared to humans, it was six times higher than that of other dinosaurs.

[1] Russell proposed that his "Dinosauroid", like members of the troodontid family, would have had large eyes and three fingers on each hand, one of which would have been partially opposed.

Gregory S. Paul (1988) and Thomas R. Holtz, Jr., consider it "suspiciously human" and Darren Naish has argued that a large-brained, highly intelligent troodontid would retain a more standard theropod body plan, with a horizontal posture and long tail, and would probably manipulate objects with the snout and feet in the manner of a bird, rather than with human-like "hands".

Their eyes were very large (perhaps suggesting a partially nocturnal lifestyle), and slightly forward facing, giving Stenonychosaurus some degree of depth perception.

The metotic strut of Stenonychosaurus was enlarged from side-to-side, similar to Dromaeosaurus and primitive birds like Archaeopteryx and Hesperornis.

[14] Stenonychosaurus are thought to have been predators, a view supported by its sickle claw on the foot and apparently good binocular vision.

[15] The jaws met in a broad, U-shaped symphysis similar to that of an iguana, a lizard species adapted to a plant-eating lifestyle.

Age determination studies performed on the Two Medicine troodont using growth ring counts suggest that this dinosaur reached its adult size probably in 3–5 years.

They were built from sediments, they were dish shaped, about 100 cm (39 in) in internal diameter, and with a pronounced raised rim encircling the eggs.

The embryos had an advanced degree of skeletal development and empty eggs were relatively uncrushed, implying that hatchlings were precocial.

From this they concluded that troodont females likely did not brood eggs, that the males did, and this may be a character shared between maniraptoran dinosaurs and basal birds.

[22] However, a later analysis of avian clutch mass found that the type of parental care cannot be determined using conventional allometric methods such as the one used by Varricchio et al.[23] Stenonychosaurus inequalis is known from the Dinosaur Park Formation of southern Alberta, Canada, which at the time was a warm coastal floodplain covered by temperate forests.

Herbivores included hadrosaurids such as Lambeosaurus, Corythosaurus, and Prosaurolophus; ceratopsids such as Styracosaurus, Centrosaurus, and Chasmosaurus; ankylosaurs such as Scolosaurus, Euoplocephalus, and Edmontonia; and pachycephalosaurs such as Stegoceras and Foraminacephale.