Remains belonging to at least ten individuals have been recovered from the Hunedoara region (Sânpetru Formation) in the area which is now western Romania. Initially they were named Titanosaurus dacus, the specific name referring to the Dacians (who had lived in that place about 2000 years ago), by Baron Nopcsa in 1915. Nopcsa had collected fossils in the area since 1895. The species was later renamed Magyarosaurus dacus by Friedrich von Huene in 1932. Von Huene in 1932 also named two other species: M. hungaricus and M. transsylvanicus. Larger, rarer M. hungaricus may represent a distinct taxon.
The holotype, BMNH R.3861a, consists of a set of vertebrae. Numerous other bones have been found, mainly caudal vertebrae but also dorsals and elements of the appendicular skeleton. No remains of skulls are known. There has been a discovery of 14 fossil eggs which have been attributed to Magyarosaurus.
Paleontology investigations have been carried out at Râpa Roșie near Sebeş, on the southwestern side of the Transylvanian Basin. The investigations were started in 1969. Dinosaur bones were reported in earlier investigations. Based on the investigations carried out by Codrea and Dica in 2005, they have assigned the age of these formations to the Early Miocene age (also conjectured as of Eggenburgian-Ottnangian age). Some of the rare fossils found here are also vertebrates and one of these is of sauropod caudal vertebra. Paleontologists involved with the studies at Râpa Roșie have also opined that this is the only sauropod genus reported at any time in the latest Cretaceous Maastrichtian formations in Romania, which could be stated as Magyarosaurus.
Magyarosaurus was estimated to be 1.1 metric tons (1.1 long tons; 1.2 short tons) in weight. It carried strange dermal armour. The estimated length of Magyarosaurus is 6 metres (20 ft), according to Curry Rogers et al..
Stein et al. (2010) found that none of Magyarosaurus close relatives had a reduced size. That means, for its clade, its small size therefore is a distinguishing autapomorphy.
A distal caudal vertebrae was named M. sp. by Codrea et al. (2008). It was probably from near the middle of the tail as it has transitional features. Before it was definitively buried, the neural arch was broken off, probably by repositioning of the vertebrae from its original position. Its centrum is elongated, and measures 105 millimetres (4.1 in) long. Both sides that would have articulated with vertebrae were severely damaged. It is assigned to Magyarosaurus on the basis that no other sauropods are known from the region it was found in, and the fact that it is located between the two vertebrae compared with it because of its intermediate morphology.