Clerck came from a family in the petty nobility and entered the University of Uppsala in 1726. Little is known of his studies; although a contemporary of Linnaeus, it is unknown whether he had any contact with him during his time in Uppsala. His limited means forced him to leave university early and enter into government service, later ending up working in the administration of the City of Stockholm.
His interest in natural history appears to have come at a more mature age, influenced by a lecture of Linnaeus he attended in Stockholm in 1737. In the following years he collected and categorized a large number of spiders, published together with more general observations on the behaviour of spiders, in his Svenska spindlar ("Swedish spiders", 1757, also known by its Latin title, Aranei Suecici). He also started the publication of Icones insectorum rariorum, a series of detailed but uncommented plates illustrating numerous species of butterflies, left unfinished after the third fascicle (1766) because of Clerck's death.
