Swiss-born scholar. In the 1750s he was tutor to the brothers of Belle de Zuylen in and near Utrecht. During his stay in Holland, he met King Frederick II the Great of Prussia who travelled incognito, and who, in 1758, called Catt to Potsdam as his personal secretary and reader, a position he held until 1780. In 1762 he married Ulrike Kühn, daughter of the Prussian envoy to St. Petersburg.
Boswell had heard about Catt from Belle de Zuylen and her family, and, on July 3, 1764, delivered a letter to him from Diederik van Tuyll. On this occasion, Boswell found Catt "dry and even insipid". In late July or early August of that same year, Boswell wrote a letter to Catt, requesting an introduction to King Frederick. Catt, in his reply, promised to mention Boswell to the King but that he could do no more, and Boswell, in fact, never was introduced to the King despite his efforts.
Catt is mostly known today for his journals from 1758 to 1760, which have been published in various editions as Henri de Catt. Vorleser Friedrichs des Grossen. Die Tagebücher 1758-1760, Friedrich der Grosse Gespräche mit Catt and Frederick the Great, the Memoirs of his Reader.