Cronstedt was born on Botby mansion (now a part of Helsinki) in Finland 3 October 1756. His parents were Johan Gabriel Cronstedt and Hedvig Juliana Jägerhorn af Spurila. He joined the army in 1765 and advanced to the rank of lieutenant in 1773. Only five years later he was promoted to the rank of lieutenant colonel. When Sweden in 1788 declared war on Russia he fought in the royal navy. In 1790 he won a great naval victory against the Russian fleet at the naval battle of Svensksund (in the Gulf of Finland). The naval battle is the greatest naval battle in the Baltic sea history.