After earning his medical degree, he spent several years working as a physician at hospitals in Heidelberg and Berlin.
During this time, he also worked closely with his brother Ernst Ruska (1906-1988) and brother-in-law Bodo von Borries (1905-56), who were both research scientists at Siemens-Reiniger-Werke.
Ernst Ruska was the inventor of the electron microscope, and later winner of a Nobel Prize.
Through close association with his brother, Helmut Ruska is remembered for developing the electron microscope for biological and medical applications.
He was the first scientist to study "sub-microscopic" structures of parasites, bacteriophages and various viruses with an electron microscope.