Similar to other anguillids, the giant mottled eel is cylindrical with small, well-developed pectoral fins and a protruding lower jaw. The eel has thick, fleshy lips. The eel has dorsal and anal fins that are continuous around the tail, with the origin of the dorsal-fin between the pectoral fins and anus. It has small, oval-shaped scales that are embedded in the skin.
Unlike some other anguillid species, this species has a mottled color. The adult eels are yellow with a greenish-brown to black marbling on their back and a white belly. The young elvers have less visible marbling and are grayish to yellow. The dorsal fin of the marbled eel is closer to the gill opening than to the anus, more anterior than other species of Anguilla. Like all anguillid eels, it does not have pelvic fins. The head is rounded and the snout is depressed. Its teeth are small and in bands. It has a total of 100 to 110 vertebrae.
It can grow up to 2 meters (6.6 ft) for females and 1.5 meters (4.9 ft) for males and can weigh up to 20.5 kilograms (45 lb), making it the largest species of anguillid eels. The marbled eel can live up to about 40 years.
Like other anguillid eels, this species is used as a source of food in some regions. Some restaurants buy live eels. In 1992, for example, a typical 12 kilogram (26.5 lb) marbled eel retailed for one thousand US dollars in China.
Large individuals of this species are also highly regarded and are not harmed by native people in some island groups of the western Pacific.