In 1870 he earned his medical degree from the University of Pavia, where he studied as an alumnus of Borromeo College. Afterwards, he joined the staff of the Ospedale Maggiore in Milan, later working as an instructor at the universities of Turin (from 1884) and Pavia (1899), where in 1900, he was appointed professor of clinical medicine.
Forlanini specialized in research of tuberculosis and respiratory disorders. He became convinced that the difficulty in curing pulmonary tuberculosis was due to the lungs being in a constant state of expansion and reduction. He realized that when these actions are removed, the "static lung(s)" would be similar to other visceral organs, and from that moment a healing process could take place. In the 1880s, he devised artificial pneumothorax for therapeutic treatment of pulmonary tuberculosis. His apparatus brought air into the lung by way of a Saugmann pneumothorax needle. An attached water manometer was employed to allow for measurement of pleural pressure and air volume. This technique is no longer in use to treat tuberculosis.
Today the "Carlo Forlanini Institute" in Rome is named in his honor.