Hyaenodon gigas was a massive, wolf-like predator and one of the largest land carnivores of its time. It measured over 10 feet (3 meters) long and likely weighed up to 1,100 pounds (500 kg). With a large skull up to 3 feet long and an incredibly powerful bite, it specialized in crushing bones and tearing through tough flesh. Its long skull held slicing carnassial teeth suited for shearing meat, and its jaws had a vice-like grip. Unlike modern carnivores, it had a more primitive brain structure but was perfectly adapted for ambush hunting and long pursuits.

It likely preyed on early ungulates, juvenile brontotheres, and anything else it could overpower. Despite its size, it may have used endurance to chase down prey or used surprise attacks in forested environments.