Roughly the size and shape of an American robin, Swainson's thrushes have olive-brown to rust-brown colored upper-parts, and a cream-colored underside with pale brown spots that are clear on the chest and become smudgier further down on the belly. They also have a pale brown ring around the eye, dull pink legs, and a medium-length brown tail. Males and females have similar color patterns.

While it can be hard to tell apart from the hermit thrush and the veery, Swainson’s thrushes can be identified among its close cousins by the buff-colored ring around its eye.

Swainson's thrushes are about 6.3-7.5 inches (16–19 centimeters) long, weighing between 0.8 to 1.6 ounces (23 to 45 grams). The average wingspan is about 12 inches (30 centimeters) in length.

Swainson's thrushes live in dense, thick forests with a mix of leafy trees and conifers. They prefer to be in areas with lots of undergrowth. While migrating, they are often spotted in forests, lake edges and suburban parks.

Their range extends across the United States during migration, stretching from Alaska and western Canada to the Atlantic Ocean, and down into the northern U.S. for the breeding season. Their wintering range extends from Mexico through Central and South America into northern Argentina. One subspecies can be found along the Pacific Coast from southern California to Alaska.

Swainson's thrushes can live up to 11 years or more, but typically about one to two years in the wild.

Swainson's thrushes have a beautiful, distinct, flute-like song that has a series of notes that seem to spiral upward. Males use this song to establish their territory during the breeding season. Males and females also have a variety of short notes they use to call out to each other or signal when a predator is nearby.

Swainson's thrushes eat primarily insects, but they will incorporate more fruits and berries into their diets during the fall and winter. They forage for food in the trees and on the forest floor, and can snatch flying insects from the air.

Swainson's thrushes are active during the daytime. During their seasonal migration, they often fly in the middle of the night.

Swainson's thrushes are mostly solitary, except when pairing up during the breeding season. During the winter, they occasionally join mixed-species flocks to forage for food.

During the breeding season, males reach the nesting grounds a few days ahead of the females, establishing their territory by singing and repelling other males. After choosing a mate, the female will build a cup-shaped nest out of twigs, moss, leaves and grasses. Females lay clutches of 3-4 pale blue eggs colored with brown spots. Incubation lasts about two weeks, and both parents care for the nestlings after hatching. After a steady diet of insects caught by their parents, the young are ready to leave the nest after about two weeks. Swainson’s thrushes will often return to the same site to breed year-over-year.

Their population is declining. Common threats include habitat loss, deforestation and fatal collisions with man-made objects, like reflective buildings and radio towers.