Reinhard Maack received his schooling in Herford, Germany, and joined the printing works of his uncle, Wilhelm Maack, in Luedenscheid. However, his thirst for adventure led him to undergo a year of practical training in surveying at the Prussian Cadastral Service and to travel to German South West Africa (now Namibia), arriving at Swakopmund in 1911. As a surveyor in the service of the colonial government he assisted in the primary triangulation of especially the coastal regions and surveyed various farms and reserves. When World War I (1914-1918) broke out he joined the Schutztruppe (colonial forces), but became a prisoner of war. He managed to escape and spent time wandering in the Kalahari before returning to South West Africa under a false name.
During February and March 1917 Maack and his colleague A. Hofmann undertook a private expedition to the Brandberg, but did not reach its highest point. The next year Maack and three others returned to the mountain and on 2 January that year succeeded in reaching the summit of Koenigstein, the highest point in Namibia at 2573 m above sea level. Theirs was the first recorded successful climb of this peak. On the way back Maack discovered the rock shelter (named Maack shelter in his honour) that contains the famous 'white lady of the Brandberg' and other rock art. A few years later he described the geology and topography of the region in 'Der Brandberg. Ein Beitrag zur Landeskunde von Suedwestafrika' (Zeitschrift der Gesellschaft fuer Erdkunde zu Berlin, 1923). An extract from his diary of his second expedition to the Brandberg was later published in the Journal of the South West African Scientific Society (1959/60, Vol. 14, pp. 5-38). His photos and descriptions of rock art in Namibia were published by H. Obermaier and H Kuehn in Germany in 1930.
In 1919 Maack undertook another expedition, this time to map the Tsondab River from Ababis to where it disappears in the Namib dune field. His account of the geology and geomorphology of the area was published as 'Die Tsondab-wueste und das Randgebirge von Ababis in Deutsch-Suedwestafrika' (Zeitschrift der Gesellschaft fuer Erdkunde zu Berlin, 1924). He distinguished clearly between older and younger Namib dune sands, being the first person to do so. In between his expeditions he lived in Swakopmund where he became known as a landscape painter.
In 1920 Maack and W.B. Volkmann* were employed by the Otavi Minen und Eisenbahn gesellschaft to report on the mining potential of the Kaokoveld, especially with regard to gold, iron and copper. After his return he was employed at the trigonometric survey office in Windhoek, but returned to Germany in 1921 to continue his studies. However, in 1923 he went to Brazil to work as a mining engineer and geological surveyor in the Minas Gerais area.
He returned to Germany in 1928 to study geography and geology at the Friedrich-Wilhelmsuniversitaet in Berlin but once again interrupted his studies to return to Brazil to work on the diamond fields at Rio Tibagi. With the idea of settling permanently in Brazil he developed a coffee plantation near Curitiba, which in due course made him financially independent. He was particularly interested in the similarity between the stratigraphy of the Parana basin in Brazil and the Karoo in South Africa, and became an early supporter of the theory of continental drift. In 1936 he returned to Germany to complete his studies. Back in Brazil he was interred during World War II (1939-1945). After his release in 1944 he was appointed as geologist at the Museum of Parana and later as director of geological and petrographic services at the Institute for Biological and Technological Research. In 1946 he published an important monograph on the geology of the Vila Velha area near Curitiba, followed during the next 17 years by five papers in German or Portuguese on continental drift and the stratigraphy of those portions of the former Gondwanaland in southern Africa and Brazil. Also in 1946 he was appointed as professor of geology and palaeontology (later physical geography) at the University of Parana in Curitiba. The Rheinische Friedrich-Wilhelmuniversitaet in Bonn awarded him a doctoral degree in 1946 for a thesis on the Gondwana glaciation of the Upper Carboniferous. He became internationally known as a geologist during the years 1952 to 1968, when he travelled widely and attended various scientific conferences. In 1957 he again visited the Brandberg in Namibia and in 1960 accompanied Dr Henno Martin on a trip to the Kaokoveld. He published an extensive monograph on the physical geography of Parana in 1968, and his last book, Kontinentaldrift und Geologie des suedatlantischen ozeans, in 1969.
Maack was an honorary member of the German Geographical Society and received its Karl Ritter silver medal in 1959. He was awarded the Jose Bonifacio de Andrade e Silva gold medal of the Geological Society of Brazil in 1967.