Chiari studied medicine in Vienna, where he was an assistant to Karl Freiherr von Rokitansky (1804–1878) and Richard Ladislaus Heschl (1824–1881).
In 1878 he received his habilitation in pathological anatomy, and within a few years became an associate professor at the University of Prague. At Prague he was also superintendent of the pathological-anatomical museum. In 1906 he relocated to the University of Strasbourg as a professor of pathological anatomy.
Chiari"s research dealt largely with postmortem examinations, and most of his numerous writings are the result of autopsies.
In the 1890s he described a condition involving deformities of the cerebellum, and brainstem in children with herniation of the spinal cord. The phenomenon was later to become known as the "Arnold-Chiari malformation", named after Chiari and German pathologist, Julius Arnold (1835–1915).
The malformation was given its name in 1907 by two of Doctor Arnold"s students. Another medical term named after Chiari is the Budd-Chiari syndrome, which is ascites and cirrhosis of the liver caused by an obstruction of the hepatic veins due to a blood clot.
lieutenant is named in conjunction with British physician George Budd (1808–1882).
Lastly, Chiari is also famous for describing the "Chiari network", an embryonic remnant found in the right atrium, first published in 1897.