Acer saccharum is a deciduous tree normally reaching heights of 25–35 m (80–115 ft), and exceptionally up to 45 m (150 ft). A 10-year-old tree is typically about 5 m (20 ft) tall. As with most trees, forest-grown sugar maples form a much taller trunk and narrower canopy than open-growth ones.

The leaves are deciduous, up to 20 cm (7.9 in) long and wide, palmate, with five lobes and borne in opposite pairs. The basal lobes are relatively small, while the upper lobes are larger and deeply notched. In contrast with the angular notching of the silver maple, however, the notches tend to be rounded at their interior. The fall color is often spectacular, ranging from bright yellow on some trees through orange to fluorescent red-orange on others. Sugar maples also have a tendency to color unevenly in fall. In some trees, all colors above can be seen at the same time. They also share a tendency with red maples for certain parts of a mature tree to change color weeks ahead of or behind the remainder of the tree. The leaf buds are pointy and brown-colored. The recent year's growth twigs are green, and turn dark brown.

The flowers are in panicles of five to ten together, yellow-green and without petals; flowering occurs in early spring after 30–55 growing degree days. The sugar maple will generally begin flowering when it is between 10 and 200 years old. The fruit is a pair of samaras (winged seeds). The seeds are globose, 7–10 mm (9⁄32–13⁄32 in) in diameter, the wing 2–3 cm (3⁄4–1+1⁄4 in) long. The seeds fall from the tree in autumn, where they must be exposed to 45 days of temperatures below 4 °C (39 °F) to break their coating down. Germination of A. saccharum is slow, not taking place until the following spring when the soil has warmed and all frost danger is past. It is closely related to the black maple, which is sometimes included in this species, but sometimes separated as Acer nigrum. The western sugar maple (Acer grandidentatum) and southern sugar maple ((Acer floridanum) are also treated as a varieties or subspecies of northern sugar maple by some botanists.

The sugar maple can be confused with the Norway maple, which is not native to America but is commonly planted in cities and suburbs, and they are not closely related within the genus. The sugar maple is most easily identified by clear sap in the leaf petiole (the Norway maple has white sap), brown, sharp-tipped buds (the Norway maple has blunt, green or reddish-purple buds), and shaggy bark on older trees (the Norway maple bark has small grooves). Also, the leaf lobes of the sugar maple have a more triangular shape, in contrast to the squarish lobes of the Norway maple.