He finished his PhD in 1938 and won a Carnegie Fellowship to study with John Carew Eccles at the Kanematsu Institute of Sydney Medical School.

He spent the war in the Pacific as a radar officer and in 1946 was invited back to UCL as an assistant director by Hill.

For three years until 1949, the Katz family lived with Hill and his wife Margaret in the top flat of their house in Highgate.

Katz was made a professor at UCL in 1952 and head of the Biophysics Department; he was elected a Fellow of the Royal Society (FRS) in 1952.

By the 1950s, he was studying the biochemistry and action of acetylcholine, a signalling molecule found in synapses linking motor neurons to muscles,[9] used to stimulate contraction.