This aquatic perennial grass can grow up to 6 metres in height. The roots and tough stalks grow from leathery horizontal rhizomes that lie on or beneath the ground surface. The stalks support broad sheath-like leaves, often 20 to 40 centimetres long and between 1 and 4 centimetres wide. Flowers develop by mid-summer and are arranged in tawny spikelets with many tufts of silky hair. The large purple flowerheads turn grey and fluffy in late summer as they go to seed.
The common reed forms dense colonies in sunny wetland habitats such as marshes, swamps, riverbanks and lake shores. The common reed can be found throughout the world.