[1][2] He spent most of his career as professor of medicine at the University of Rome (now Sapienza Università di Roma).

He gave a complete description of a genetic disease of blood now known Paroxysmal nocturnal hemoglobinuria or sometimes Strübing-Marchiafava-Micheli syndrome, in honour of the pioneer scientists.

He served as personal physician to three popes, Leo XIII, Pius X and Benedict XV.

[4] Marchiafava first developed his first research interest in pathology from Robert Koch, whom he met in Berlin during his doctoral course.

[5] They were the first to use proper staining (with methylene blue) to identify malarial parasite as distinct blue-coloured pigments in the blood cells.

They showed that the parasites lived inside blood cell, and that they divide by simple splitting (fission).

[7][8] Marchiafava was the author of Sulle febbri malariche estivo-autunnali (1892) and La infezione malarica (1902).

In 1884, with Angel Celli, he first observed Gram-negative diplococci in the cerebrospinal fluid of a fatal case of meningitis in 1884.

In 1931, he described Paroxysmal nocturnal hemoglobinuria in depth, and also a rare form of this disease Strübing-Marchiafava-Micheli Syndrome.