Gustav Bloch, his father, was financially unable to attend University and worked as a wholesale grain dealer in Zürich.

[4] Bloch entered public elementary school at the age of six and is said to have been teased, in part because he "spoke Swiss German with a somewhat different accent than most members of the class".

[4] He received support from his older sister during much of this time, but she died at the age of twelve, devastating Felix, who is said to have lived a "depressed and isolated life" in the following years.

On March 14, 1940, Bloch married Lore Clara Misch (1911–1996), a fellow physicist working on X-ray crystallography, whom he had met at an American Physical Society meeting.

[5][7] Bloch remained in European academia, working on superconductivity with Wolfgang Pauli in Zürich; with Hans Kramers and Adriaan Fokker in Holland; with Heisenberg on ferromagnetism, where he developed a description of boundaries between magnetic domains, now known as "Bloch walls", and theoretically proposed a concept of spin waves, excitations of magnetic structure; with Niels Bohr in Copenhagen, where he worked on a theoretical description of the stopping of charged particles traveling through matter; and with Enrico Fermi in Rome.

[5] In 1933, immediately after Hitler came to power, he left Germany because he was Jewish, returning to Zürich, before traveling to Paris to lecture at the Institut Henri Poincaré.

In the fall of 1938, Bloch began working with the 37 inch cyclotron at the University of California, Berkeley to determine the magnetic moment of the neutron.

Disliking the military atmosphere of the laboratory and uninterested in the theoretical work there, Bloch left to join the radar project at Harvard University.