Greererpeton had an elongated body adapted for swimming, reaching up to 1.5 metres (4.9 ft) in length, including the tail. Its body had 40 vertebrae, twice the usual amount, and a flattened skull about 18 centimetres (7.1 in) long. The limbs were short, and mainly used for steering, with the long tail providing the main propulsive force while swimming.
Some marks on the side of the skull indicate that Greererpeton had a lateral line, a sensory organ commonly found only in fish. Its ears were also poorly developed. Taken together, these are indications that Greererpeton was a primitive amphibian that had returned to an almost wholly aquatic existence, rarely, if ever, venturing onto dry land.
Greererpeton was a carnivore and probably lived in rivers and swamps.