Vigna marina is a somewhat succulent creeping or climbing perennial herb that can grow up to several meters long, becoming woody toward the base and is sparsely to densely pubescent. The leaves are compound (pinnately trifoliolate or occasionally unifoliolate) and alternate, with 3.5–10.5 cm long leaflets and 2.5–8.8 cm wide. The leaflets are rhombic–elliptic to broadly rhombic–ovate or obovate, with an apex rounded to emarginate. The surfaces are sparsely appressed pilose and soon become glabrate, with entire margins. The leaves are petiolate, and the stipules are peltate and truncate. The flowers are slightly waxy and arranged in 6.3–14 cm long racemes with 4.3–10.5 cm long peduncles. The flowers are papilionaceous, with bracteoles present and pedicels that are 4.5–6 mm long. The calyx is green, tinged reddish, with the upper two lobes completely connate, forming an entire upper lip 1.8–2 mm long, lateral lobes deltate, about 1.5 mm long, and the lowest tooth deltate, about 2 mm long, all glabrous. The calyx is bilabiate with five lobes, and the lower lip is 3-lobed. The corolla is green in bud and bright yellow at anthesis, 12–19 mm long, with the standard very broadly obcordate and reflexed, and the keel not beaked, incurved about 1/2 turn or less. There are ten stamens, with the upper stamen distinct and the other nine connate into a tube. The ovary is superior, with styles bearded below the stigma along the inner edge, and the stigma is lateral. The fruit consists of linear–oblong pods that are inflated, slightly curved, 35–60 mm long, and 8–9 mm wide. The pods are glabrous and slightly constricted between the seeds. The seeds are 2–10 in number, yellowish brown to reddish brown, reniform or broadly ellipsoid, 6–7 mm long, 4.5–6 mm wide, slightly compressed, with an oblong hilum and a scarcely developed rim-aril. It occurs at the vegetation line on sandy beaches and is rarely found somewhat inland on sea cliffs and dry shrubby slopes between 0-120 meters.