Tennessee warblers are tiny, greenish birds with short tails and sharply pointed bills. Males in their breeding colors are marked by their gray heads with a white line over the eye, yellowish-green back and whitish-gray belly. Females generally show more yellow, especially on the underside. They are often mistaken for the orange-crowned warbler but can be distinguished by their white undertail feathers.

Adults are about 4.5 inches (11.5 centimeters) long.

They can be found in woodlands, forest edges, and shrubby areas, typically high above the ground. During migration they are often found among flowering trees; in their wintering areas, they favor shaded coffee farms and plantations. 

In the spring and summer, these birds migrate from their winter homes in Central and South America to their breeding grounds in the northern United States and Canada, passing through much of North America along the way. Occasionally, vagrants are found in northern Europe.

The oldest known bird was 6 years old, but most probably live 1-2 years.

Male warblers have a loud, sharp chirping song that they use to establish their territory and attract females. 

During the breeding season, insects make up the bulk of their diet. They forage for caterpillars, beetles, and other insects high in the forest canopy. A common prey animal is the spruce bedworm.

During migration and winter, Tennessee warblers will expand their diets to include berries and nectar. Often referred to as "nectar thieves," they feed by poking a hole in the bottoms of flowers to drain out and drink nectar without contributing to the flower's pollination.

During spring and fall migration, Tennessee warblers form into mixed-species flocks.

Many aspects of the Tennessee warbler's breeding status are not well known, due to the remoteness of the boreal forest habitats where they reproduce. Females often build nests in boggy ground, hidden in small depressions among bushes and other vegetation. Nests resemble an open cup and are made from thin grass stems and animal hair. They lay between four to seven eggs, which the female incubates for 11-12 days. 

The International Union for Conservation of Nature does not consider Tennessee warblers to be especially at risk. However, like many birds that migrate at nighttime, individuals are threatened by collisions from man-made objects, like radio towers and reflective skyscrapers.