Dr. Otto Rahn was born in Tiegenhof in West Prussia (now Poland) between Danzig and Elbing in 1881 as third of eleven children to Isbrand Rahn, a Mennonite storekeeper, and Marie (Claassen) Rahn. After originally planning to enter the ministry, by the end of high school he decided to pursue chemistry and mathematics. In 1899 he began studying at the University of Göttingen, majoring in organic chemistry. He received a Ph.D. cum laude on December 24, 1902.

Dr. Rahn worked as assistant in Dairy Science at Göttingen from 1902 to 1906, and also did research on the biochemistry of bacterial growth. After being denied an instructing position, he left Göttingen and became an assistant at the Agricultural Experiment Station at Halle. He corresponded frequently with bacteriologists in the United States and was offered an assistant professorship in bacteriology at Michigan State College in 1907. Rahn married his assistant, Belle Farrand, on September 4, 1911, in Lansing, Michigan. In 1912, he left Michigan for the University of Illinois, where he built a strong department over the course of two years. In 1914, after seven years away from home, Rahn took his family to Germany to meet his relatives.

World War I broke out while Dr. Rahn was still a German citizen, unable to complete the requirements for American citizenship. He and his family were trapped in Germany for the next twelve years, and Rahn had to run the family hotel until he was drafted and worked at an airplane station in Latvia, struggling to complete his work during his spare time. This work was published much later, but helped him establish a bacteriology career in Germany.

Upon dismissal in 1918 he returned to his family in Danzig with neither a job lead in Europe nor way of returning to America. In 1919 he received an assistantship position in the Agricultural College in Berlin before being appointed Director of the Physical Chemistry Department (later the Department of Physics) in 1920 at the Prussian Experimental and Research Institute for Dairying in Kiel. He became Verwaltungsdirektor of the Institute in 1925. By reaching the requirements at the University of Kiel, he was able to become an instructor and remained entitled to this right until his death. At Kiel he did research on the fat in milk that explained the process of butter churning that was previously understood.

Dr. Rahn's work in dairy intrigued American investors, who invited him to lecture around the country. After a year of this, Cornell University offered him a position as Professor of Bacteriology. His laboratory here became renowned for research in fermentation, growth cycles, and biological radiation. Because he preferred to work with numbers and data at his own desk, he became a resource for developing ideas for assistants and graduate students. An avid reader and enthusiastic learner, he was highly respected as a teacher and researcher.

In 1949 at the age of 68, Rahn retired from Cornell University but worked at Idaho State College until 1954. After leaving Idaho State College, he and his wife moved near their daughter, Margarete, in Delaware. There he died on September 26, 1957.