Johann Deisenhofer (born September 30, 1943) is a German biochemist who, along with Hartmut Michel and Robert Huber, received the Nobel Prize for Chemistry in 1988 for their determination of the structure of a membrane-bound complex of proteins and co-factors that is essential to photosynthesis.

Deisenhofer earned his doctorate from the Technical University of Munich for research work done at the Max Planck Institute for Biochemistry in Martinsried, West Germany, in 1974. He conducted research there until 1988, when he joined the scientific staff of the Howard Hughes Medical Institute and the faculty of the Department of Biochemistry at The University of Texas Southwestern Medical Center at Dallas.
Between 1982 and 1985, Michel and Huber, Deisenhofer used X-ray crystallography to determine the exact arrangement of the more than 10,000 atoms that make up the protein complex.
Deisenhofer currently serves on the board of advisors of Scientists and Engineers for America, an organization focused on promoting sound science in American government.