It is a medium-sized deciduous tree growing to 18-22 m (60-70 ft) tall, with a trunk up to 1 m (3 ft) diameter. It has an 8-14 m (25-45 ft) spread. A 10-year-old tree will be about 8 m (25 ft) tall. The crown is broad conic when young, with numerous small branches radiating out from a central leader. When older, some upper branches become quite large and the central leader is lost, while the lower branches gradually droop downwards.

The leaves are 5-16 cm long and 5-12 cm broad, lobed, with five or seven lobes, and deep sinuses between the lobes. Each lobe has 5-7 bristle-tipped teeth. The leaf is mostly hairless, except for a very characteristic tuft of pale orange-brown down on the lower surface where each lobe vein joins the central vein. The acorns, borne in a shallow cup, are hemispherical, 10-16 mm long and 9-15 mm broad, green maturing pale brown about 18 months after pollination; the kernel is very bitter.

It is not a long-lived tree, usually living only 90 to 120 years. It is naturally a wetland tree, and develops a shallow, fibrous root system, unlike many oaks, which have a strong, deep taproot when young. It is confined to acidic soils, and does not tolerate limestone, and grows at low altitudes from sea level up to 350 m. The specific name palustris means “of swamps”.

A feature of Pin oak (shared by a few other oak species, and also some beeches and hornbeams) is the retention of leaves through the winter on juvenile tissue. Young trees under 6 m (20 feet) will often be covered with leaves year-round, though the leaves die in the fall, remaining attached to the shoots until the new leaves appear in the spring. As with many other oak species, dead Pin oak branches will stay on the tree for many years.