Georg Grossarth was educated at the secondary school in Sobernheim, in the south-west of Germany. While still at school his uncle, Daniel Haeberle, professor of palaeontology at Heidelberg, inspired him to collect Permian fossils of amphibia. In 1904 he came to German South West Africa (now Namibia) to complete his military service in the German Schutztruppe (colonial troops). Owing to the war between Germany and the Hereros he remained in military service for two years, during which time he came to know most of the colony. He managed to make a collection of fossils from the Ecca Group while still in military service, but as the finds could not be transported on horseback they were lost. However, during a later journey in the same region he collected, among others, fossils of the aquatic reptile Mesosaurus and presented his finds to the State Museum in Windhoek. The museum also has specimens of the bivalve shell Eurydesma and various echinoderms that he collected from the Dwyka Group at Mariental, and a number of fossil species that he collected from Permian strata near his birthplace, Odernheim. Other specimens collected by him are in the British Museum and in Berlin. During a journey he undertook with the curator of the Windhoek museum he obtained for it various cultural artefacts of the San (Bushmen), including a bark quiver.
As the museum in Windhoek did not have a trained palaeontologist or preparators, Grossarth sent most of his fossils to Germany, where they ended up in the museum in M?nchen. Later he undertook travels in South Africa to collect fossils for the Institute f?r Palaeontologie in M?nchen, with considerable success. His finds were described by F. Broili and J. Schr?der in the Sitzungsberichten der Bayrischen Akademie der Wissenschaften, including two new genera and several new species. One of these was named Gomphoynathus Grossarthi, after the collector. His most important find was a specimen of the mammal-like reptile Tritylodon Oweni, from the Stormberg beds near Clarens in 1935, which included fragments of the animal's milk teeth - the first such find in vertebrates of Karoo age. He became well known among palaeontologists as a fossil collector and in June 1936 the Bayerische Akademie der Wissenschaften honoured him with the presentation of a silver medal.
Grossarth became a member of the South West Africa Scientific Society in 1932. In spite of his extensive knowledge and important finds his introverted nature ensured that he was not widely known among the general public. He married the widow Margarete Michaelis, with whom he had a daughter who also became a fossil collector.