He was born in Hamburg, and did research in Germany and in the United States regarding quantum physics. In 1925, he received the Nobel Prize in Physics, mostly for his work in 1912-1914 which included the Franck-Hertz experiment, an important confirmation of the Bohr model of the atom. In 1933, after the Nazis came to power, he left his post in Germany and continued his research in the United States, first in Baltimore and then, after a year in Denmark, in Chicago. This is where he became involved in the Manhattan Project during World War II. He was the chairman of the Committee on Political and Social Problems regarding the atomic bomb; the committee consisted of himself and other scientists at the Manhattan Project's Metallurgical Laboratory at the University of Chicago, including Donald J. Hughes, J. J. Nickson, Eugene Rabinowitch, Glenn T. Seaborg, J. C. Stearns and Leo Szilard. The committee is most known for the compilation of the Franck Report, finished on June 11, 1945, which was a summary of the problems regarding the military application of the Atomic Bomb.
When Germany invaded Denmark in World War II, the Hungarian chemist George de Hevesy dissolved the gold Nobel Prizes of Max von Laue and James Franck into aqua regia to prevent the Nazis from stealing them. He placed the resulting solution on a shelf in his laboratory at the Niels Bohr Institute. After the war, he returned to find the solution undisturbed and precipitated the gold out of the acid. The Nobel Society then recast the Nobel Prizes using the original gold
- http://nobelprize.org/physics/laureates/1925/franck-bio.html biography, on the Nobel website