During the Great Patriotic War, Oleg Gavrilov, as a surgeon, a senior doctor of the regiment and brigade physician of the Airborne Troops, took part in the fighting on Karelian and 3rd Ukrainian fronts. After the end of the war he served as division physician in the Airborne Division in the Far East.
In 1955 Oleg Gavrilov defended his Candidate thesis, and in 1965 - his doctoral thesis on the problems of military medicine and blood services in the Armed Forces. In 1967, Oleg Gavrilov was awarded the academic title of professor. He was a Colonel of the medical service. After the end of military service, he worked as a vice-principal on medical work of the 1st Moscow Medical Institute, as a director of the Central Institute of Hematology and Blood Transfusion in Moscow, as a chairperson of the Scientific Medical Council of the Ministry of Health of the USSR.
In 1974 Oleg Gavrilov was elected a corresponding member, and in 1982 he was elected a full member of the Academy of Medical Sciences of the USSR.
Oleg Gavrilov is also a member of the international societies of hematologists and transfusiologists, an honorary member of the Society of Hematology and Transfusiologists of Hungary, an honorary member of the Medical Society named after Jan Evangelist Purkinje (Czech Republic).
Currently, Oleg Gavrilov leads the academic group. He is a scientific consultant of the Research Complex of Blood Surgery, a member of the Bureau of the Department of Clinical Medicine of the Russian Academy of Medical Sciences, and is a member of the editorial board of several medical journals, including foreign ones.