He was proficient in mathematics and physics as a child, and encouraged by his family to become an engineer or architect. However, he was more interested in world history, and chose to pursue an academic career over their wishes and studied at the University of Berlin under the renowned historian, Leopold von Ranke.
In 1884 Riess traveled to Great Britain and Ireland for the purpose of collecting materials for his doctoral dissertation "The vote of the British Parliament in the medieval ages", and received his doctorate at the age of 24.
He returned to the British Isles again in 1885 and 1886 to collect additional materials pertaining to German history and the Hanseatic League.
Riess was recruited as a foreign advisor by the Meiji government of the Empire of Japan in 1887 to establish Western methods of historiography into the Japanese university curriculum.
Riess taught history and geography at Berlin University before accepting an offer by the Japanese Government to teach Western history at Tokyo University (1887). The study of Western history began with his arrival for the first time in Japan. He returned home for a vacation (1893) and when he came back he brought a lot of historical material which proved of great value to academic circles in Japan. Later he founded a historical society.
Riess returned to the German Empire in 1902, and taught as an assistant professor at the University of Berlin.
In 1904, during the Russo-Japanese War, there was tremendous interest in Germany about all things Japanese, and Riess was in constant demand for articles about Japan and Japanese people for the German newspapers. During this period he published an autobiography the "Allerlei aus Japan" about his 15 years experiences in Japan.
In 1926, Reiss visited Springfield, Ohio in the United States as an exchange teacher. Soon after arrival, he developed a fever, possibly due to allergic reaction after being stung by an insect, and died at the age of 67.
In 1888, Riess married a Japanese woman, Fuku Ōtsuka, the daughter of his cook, with whom he had one son and four daughters.