Koch began his career as a general practitioner in Langenhagen near Hanover, then moved to Niemegk. While practicing medicine, he continued to pursue his scientific interests independently.

Koch volunteered as a physician in the Franco-Prussian War, working in military hospitals. This experience exposed him to infectious diseases, further fueling his interest in their causes and prevention.

Koch became the district physician in Wollstein (present-day Wolsztyn, Poland). With limited resources, he established a small laboratory in his home and dedicated himself to studying infectious diseases, notably anthrax. This was a crucial period where he developed his innovative techniques.

Koch achieved his first major breakthrough with his detailed study of anthrax. He isolated "Bacillus anthracis", demonstrated its life cycle (including spore formation), and proved that it caused the disease by inoculating animals. This was a landmark achievement that firmly established the germ theory of disease.

Koch pioneered the use of staining techniques and photomicrography to visualize and document bacteria. He developed methods for fixing, staining, and photographing bacteria, making them much easier to study under the microscope. These techniques were crucial for his subsequent research.

Koch's groundbreaking work on anthrax earned him recognition from the scientific community, and he was appointed to the Imperial Health Office in Berlin. This provided him with access to better resources and a team of researchers.