Johan was the nephew of the famous marine artist Carl Neumann (1833-1891), and received most of his training by him. Like his uncle Carl, Johan Neumann was a marine artist and worked primarily with seascapes and ship portraits. Johan worked most of his life outdoors and often traveled to the coast of Skagen and to the Ise Fjord in western Jutland. Johan Neumann was known for his detailed portrays of the famous Frigate Jutland and for his series of shore side works with smaller fishing vessels. Johan was also known for his historical seascapes, where he portrayed the many famous sea battles in Nordic history. Johan worked primarily all over the Scandinavian coastlines but traveled and worked in Island from 1892. The works of Johan Neumann has been exhibited numerous times in most Scandinavian and European marine and nautical museums.