Its fossils were found in the Neuquén province of Argentina in 2000, and were scientifically described in 2007. The genus name is derived from the local indigenous language Mapudungun and is pronounced foo-ta-long-koh-sohr-us: "futa" means "giant" and "lognko" means "chief". It is based on three fossil specimens, yielding an estimated 70% of the skeleton in total. The fossil team described the find as "the most complete giant dinosaur known so far".
The type species, Futalognkosaurus dukei, is estimated to be 26 m (85 ft) in length, rivaling the gigantic Argentinosaurus. Its long neck contained 14 vertebrae, and was over a meter deep in places, due to its extremely tall neural spines which had a distinctive "shark-fin" shape. The hips were also extremely large and bulky, reaching a width of nearly 3 metres (9.8 ft). The alternate early spelling "Futalongkosaurus" may be found in some press reports and on websites.