It stood 2.8 metres (9 ft) tall and looked like a robust version of the modern elephant. It weighed about 6,000 kilograms (13,000 lb). Like modern elephants, but unlike most of its closer relatives, it had just two tusks. These tusks curved upwards and were about 3.5 metres (11 ft) long. Stegomastodon's molars were covered in enamel and had a complex pattern of ridges and knobbly protrusions on them, giving the creature a large chewing surface that enabled it to eat grass. It lived in North and South America, and its brain weighed about 11 pounds (5 kg).
The two South American species arrived following the Great American Interchange. They were initially mixed feeders; S. waringi evolved towards grazing, while S. platensis evolved towards browsing. The Stegomastodon species occupied warmer, lower-altitude habitats east of the Andes, while the related gomphothere Cuvieronius hyodon occupied cooler, higher-altitude habitats.