This adventive biennial plant is a low-growing rosette of basal leaves during the first year, but during the second year it becomes 3-6' tall. The second-year plant is little branched below, but produces short flowering side stems above. The stems are rather stout, round or slightly ridged in circumference, and light green to slightly reddish green. Young stems are covered with white cobwebby hairs, but older stems become glabrous and have conspicuous longitudinal veins. The basal leaves are up to 2' long and 1½' across. They have long petioles and resemble the leaves of rhubarb to some extent. The lower leaves of second year plants resemble the basal leaves, except that they are somewhat smaller. These leaves are ovate-cordate, dull green above, and whitish green below, with blunt tips. They are nearly glabrous above, but finely pubescent below. Their margins are somewhat undulate, crisped, or smooth, sometimes with a few blunt teeth. Their long petioles have a conspicuous furrow above and they are usually hollow inside. The middle to upper leaves of second year plants are similar in appearance, but they are smaller in size and more likely to be ovate with margins that are more smooth and petioles that are shorter. The upper stems terminate in small clusters of flower heads on short stalks. Each flower head is about ¾–1" across, consisting of numerous disk florets and floral bracts that have narrow hooked tips. There are no ray florets. Each disk floret has a corolla that is narrowly cylindrical with 5 slender upright lobes at the apex. The disk florets are usually some shade of pink or purple, although a rare form of Common Burdock with white florets occurs. The slender white style is strongly exerted from the corolla and bifurcated at its tip. The dark purple anthers form a sheath around the style that lies just above the lobes of the corolla. The abundant bracts are green at the base, but become yellowish green toward the their hooked tips. They have a spiny appearance and have few, if any, cobwebby hairs in their midst. The blooming period occurs from mid-summer to early fall, and lasts about a month for a colony of plants. The achenes are oblong, broader and more truncate at one end than the other, and light brown with dark brown speckles. At the apex, each achene has a crown of fine bristles, but these are deciduous and soon fall off. The floral bracts turn brown and enclose the withered flowers at the top, forming a bur. The burs are persistent and remain on the stalks after the leaves have withered away during the fall. The root system consists of a stout taproot that runs deep into the ground. This plant spreads by reseeding itself, and often forms colonies of variable size.

The foliage of Common Burdock is one of the food sources for the caterpillars of the butterfly Vanessa cardui (Painted Lady). The Ring-Necked Pheasant eats the seeds to a limited extent. Because the foliage is bitter-tasting, Common Burdock is not a preferred food plant for mammalian herbivores, although livestock and deer will browse on it if nothing else is available. There is some evidence that the foliage may be toxic to rabbits. The seeds are distributed far and wide by animals and humans because the burs cling readily to fur and clothing. They are quite difficult to remove.