Pinus banksiana ranges from 9–22 m (30–72 ft) in height. Some jack pines are shrub-sized, due to poor growing conditions. They do not usually grow perfectly straight, resulting in an irregular shape similar to pitch pine (Pinus rigida). This pine often forms pure stands on sandy or rocky soil. Many populations are adapted to stand-replacing fires, with the cones remaining closed for many years, until a forest fire kills the mature trees and opens the cones, reseeding the burnt ground. Other populations have not been shaped by regular stand-replacing fires and have reduced serotiny. A population on the Maine coast is apparently not reliant on fire for reproduction, and some stands have developed several age classes. Populations with lower serotiny are often found on soils that are in some way limiting to faster-growing competition, such as soils shallow to bedrock, shallow to water table, or very young soils.

Its leaves are needle-shaped, evergreen, in fascicles of two, needle-like, straight or slightly twisted, stiff, sharp-pointed, light yellowish-green, spread apart; edges toothed and 2–4 cm (3⁄4–1+1⁄2 in) long. The bundle-sheath is persistent. The buds are blunt pointed, up to 15 mm long, reddish-brown, and resinous. On vigorous shoots, there is more than one cyclic component. The bark is thin, reddish-brown to gray in color in juvenile stages. As the tree matures it becomes dark brown and flaky. The wood is moderately hard and heavy, weak, light brown colour. The seed cones vary in shape, being rectangular to oval, cone shaped, straight or curved inward. The cones are 3–5 cm (1+1⁄4–2 in) long, the scales with a small, fragile prickle that usually wears off before maturity, leaving the cones smooth.

Unusually for a pine, the cones normally point forward along the branch, sometimes curling around it. That is an easy way to tell it apart from the similar lodgepole pine in more western areas of North America. The cones on many mature trees are serotinous. They open when exposed to intense heat, greater than or equal to 50 °C (122 °F). The typical case is in a fire, however cones on the lower branches can open when temperatures reach 27 °C (81 °F) due to the heat being reflected off the ground.