Vicia sativa is a sprawling annual herb, with hollow, four-sided, hairless to sparsely hairy stems which can reach two meters in maximum length.
The leaves are stipulate, alternate and compound, each made up of 3–8 opposite pairs of linear, lance-shaped, oblong, or wedge-shaped, needle-tipped leaflets up to 35 millimetres long. Each compound leaf ends in a branched tendril.
The pea-like flowers occur in the leaf axils, solitary or in pairs. The flower corolla is 1–3 centimetres long and bright pink-purple in colour, more rarely whitish or yellow. The flowers are mostly visited by bumblebees.
The fruit is a legume pod up to 6 or 7 centimetres long, which is hairy when new, smooth later, then brown or black when ripe. It contains 4–12 seeds.