Vicia menziesii is a coarse, climbing perennial herb that can grow between 1.5 and 20 meters long, typically supported by the canopy of trees or shrubs. When young, it is pubescent but becomes sparsely so with age. The leaves are compound and alternate, with 8–12 leaflets that are narrowly ovate to oblong-ovate, measuring 35–70 mm in length and 15–30 mm in width. These leaflets have acute to rounded and mucronate apices, sparsely pubescent surfaces, and lacerate-dentate margins with subulate teeth. The plant features semi-sagittate, foliaceous, and suborbicular stipules, which are 20–30 mm long and 10–20 mm wide. The flowers are papilionaceous, presented in axillary racemes of 6–9 flowers each, with minute, caducous bracts and 8–10 mm long pedicels. The calyx is gibbous with five lobes, and the corolla transitions from ochreoleucous (yellowish-white) when young to purple, measuring 25–30 mm with a curved style that is dorsoventrally flattened and surrounded by short hairs that become longer toward the stigma. The standard petal has a broad claw, with wing petals obliquely oblong and keel petals shorter than the wings. It has ten stamens, with the upper one distinct or adhering with the others and the remaining 9 forming a tube. The fruit is a black oblong-ellipsoid pod at maturity, 90–100 mm long and 15–20 mm wide, stipitate, laterally compressed, and dehiscent, containing black, globose seeds 7–8 mm in diameter, with the hilum extending ca. 3/4 of the circumference. It occurs in wet to mesic forests or open, decadent forests with a fern understory between 1,570-1,720 meters.