Orbeli played an important part in the development of evolutionary physiology and wrote more than 200 works on experimental and theoretical science, 130 of them journal articles.
Orbeli graduated from the Military Medical Academy in 1904 and became an intern at the Nikolai Hospital in Kronstadt, the Naval Hospital in Saint Petersburg. This gave him the opportunity to continue his experimental research in Pavlov's laboratory.
Orbeli's scientific career was spent in the leading Russian physiological centres, and he joined Pavlov in 1907, at the very height of Pavlov's research on conditioned reflexes. He was Pavlov's assistant in the Department of Physiology at the Institute for Experimental Medicine from 1907 to 1920.
In 1956, Orbeli organized the I. M. Sechenov Institute of Evolutionary Physiology and headed this institution until 1958. It was later renamed I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry of the Academy of Sciences of the Soviet Union. In 1935 he was elected an active member of the Academy of Sciences of the Soviet Union. In 1945 he was awarded the title of Hero of Socialist Labour. He held the rank of colonel general.