After attending the Faculty of Medicine of the University of Bucharest, Marinescu received most of his medical education as preparator at the laboratory of histology at the Brâncoveanu Hospital and as assistant at the Bacteriological Institute under Victor Babeș, who had already published several works on myelitis transversa, hysterical muteness, and dilatation of the pupil in pneumonia.

After qualification, and on the recommendation of Babeş, the government awarded Marinescu a grant to undertake postgraduate training in neurology under Jean-Martin Charcot at the Salpêtrière Hospital in Paris, where he met Pierre Marie, Joseph Babinski, and Fulgence Raymond.

Daily contact with scores of the infirm and his astuteness made him use the latest methods as they became available, such as the X-ray, with which he investigated bone changes in acromegaly, and the film camera, for the study of body movements in health and disease.

The results of these studies appeared in the monograph Le Tonus des Muscles striés (1937) with Nicolae Ionescu-Siseşti, Oskar Sager and Arthur Kreindler, with a preface by Sir Charles Scott Sherrington.

Early in his career, Marinescu published a much needed atlas on the pathological histology of the nervous system with the bacteriologist Victor Babeş and the French pathologist Paul Oscar Blocq.