After study at Uppsala and Greifswald, Leopold began his career in 1792 with skillful articles and polemical essays propagating the rational ideas of the Enlightenment and parrying the criticism of the younger generation of Romantics (Romanticism). He was disliked by the early Romantics in Sweden because of his opposition to their work. A member of the Swedish Academy from its foundation in 1786, he became, on the death of the poet and critic Johan Henric Kellgren (Kellgren, Johan Henrik) (1795), the dominant arbiter of classical taste in Sweden. He also replaced Kellgren as Gustav's principal librettist. (The king wrote prose dramas that Kellgren and then Leopold converted into verse for operas.) Leopold's philosophical, didactic poetry is typified by his ode "Försynen" (1793; “Providence”), but his best-known poem is probably "Predikaren" (1794; “The Sermonizer”), notable for its cynical portrait of courtiers.

Leopold was given noble rank in 1809. His last years were saddened by his wife's insanity and by his own blindness.