Sebastes elongatus has a comparatively slender, elongated, scaly, body which has a depth of around one-third of its standard length with a moderately sized head and eyes. There are venom glands in the spines of the dorsal, anal and pelvic fins. The caudal fin is truncate to weakly crescent shaped. On the head the nasal, preocular, postocular, tympanic and parietal spines are robust and present while the supraocular, coronal and nuchal spines are absent. The dorsal fin has 13 spuines and 12-14 soft rays while the anal fin has 3 spines and 6 soft rays. This species attains a maximum total length of and a maximum published weight of . The color of the body is white to reddish marked with four very clear longitudinal green stripes, two either side of the lateral line. There is green streaking on the membranes of the caudal fin membranes with a red streak on the maxilla.
