The common hawthorn is a shrub or small tree 5–14 metres (15 to 45 feet) tall, with a dense crown. The bark is dull brown with vertical orange cracks. The younger stems bear sharp thorns, approximately 12.5mm (half an inch) long. The leaves are 20 to 40mm (1 to 1½ inches) long, obovate and deeply lobed, sometimes almost to the midrib, with the lobes spreading at a wide angle. The upper surface is dark green above and paler underneath.
The hermaphrodite flowers are produced in late spring (May to early June in its native area) in corymbs of 5-25 together; each flower is about 10mm diameter, and has five white petals, numerous red stamens, and a single style; they are moderately fragrant. The flowers are pollinated by midges, bees and other insects and later in the year bear numerous haws. The haw is a small, oval dark red fruit about 10mm long, berry-like, but structurally a pome containing a single seed. Haws are important for wildlife in winter, particularly thrushes and waxwings; these birds eat the haws and disperse the seeds in their droppings.
The common hawthorn is distinguished from the related but less widespread Midland hawthorn by its more upright growth, the leaves being deeply lobed, with spreading lobes, and in the flowers having just one style, not two or three. However they are inter-fertile and hybrids occur frequently; they are only entirely distinct in their more typical forms.