Lycodes esmarkii is an elongate species reaching up to 70 cm in length. The body tapers gradually backwards from the origin of the anal fin. The dorsal fin originates over the pectoral fins and runs continuously over the back to the tail and is joined to the anal fin. The anal fin itself then runs forwards on the underside three fifths of the body length. Very small pelvic fins are present. The pectoral fins are only slightly rounded. The lateral line is double, with ventral and midlateral branches. The eyes are large and the mouth is subterminal. Upper body colouration is dark brown with 5-9 whitish marks (often an inverted Y-shape), while the underside is lighter.