Born in Rota d'Imagna near Bergamo to an Italian noble family, Quarenghi was destined by his parents for a career in law or the church but initially was allowed to study painting in the Bergamo studio of G. Reggi, himself a student of Tiepolo.
His work in Italy and for English clients formed enough of a reputation that in 1779 he was selected by the Prussian-born count Rieffenstein, who had been commissioned by Catherine II of Russia to send her two Italian architects to replace her French ones (Loukomsky 1928).