Delbrck studied astrophysics, shifting towards theoretical physics, at the University of Gttingen. After receiving his Ph.D., he traveled through England, Denmark, and Switzerland. He met Wolfgang Pauli and Niels Bohr, who got him interested in biology. Delbrck went back to Berlin in 1932 as an assistant to Lise Meitner.
In 1937, he moved to the United States, taking up research at Caltech on genetics of the fruit fly Drosophila melanogaster. Delbrck stayed in the US during World War II, teaching physics at the Vanderbilt University in Nashville.
In 1939, he co-authored a paper called The Growth of Bacteriophage with E.L. Ellis in which they demonstrated that viruses reproduce in "one step ", rather than exponentially as cellular organisms do.
In 1941, he married Mary Bruce, with whom he had four children.
In 1942, he and Salvador Luria demonstrated that bacterial resistance to virus infection is caused by random mutation and not adaptive change. For that, they were awarded the Nobel Prize in Physiology or Medicine in 1969, sharing it with Alfred Hershey.
See also: Luria-Delbruck experiment