Ljungh was born on Björkö Prestgård in Småland to provost and priest Sven Ljlungh and Brigitta Oxelgren.
He was educated at home until 1770 before studies under the lexicographer Håkan Sjögren from whom he learned the Latin language.
He took up a position in the Swedish civil service as a clerk in the judicial system and in 1778 became the Deputy Crown Bailiff in North and South Vedbo.
[1][2] He was a scholar who exchanged correspondence with many contemporary scientists including Carl Thunberg, G Marklin, Erik Acharius, Fr Ehrhart, Jan Brandes and others.
In 1803 his insect collection had an estimated 5000-6000 species and he published many notes on exotic animals from Java, Ceylon and the Cape.