One of the founders of Nitroglycerin Aktiebolaget (later Nitro Nobel), Smitt was Chairman of the Board from 1864 to 1904. In the 1850s Smitt amassed a fortune in South America. He liquidated his assets in 1856 and returned to Stockholm. There, his prudent property investments, particularly in the Kungsholmen district, earned him the sobriquet "King of Kungsholmen". He was regarded as Stockholm's richest man in the 1860s, and later was Argentina's Consul General in the Swedish capital. In 1866 he became a councilor in the Stockholm City Council and sat on the boards of several major companies.