 Following the defeat of the insurrection in the Austrian Netherlands, he received permission from Field Marshal Laudon, shortly before the latter's death, to take a one year novitiate in the Teutonic Order, at Bonn where he remained until April 1792. The outbreak of the War of the First Coalition against France required his military talents and Mervelt rejoined the Habsburg army at as adjutant to Josias, Prince of Saxe-Coburg-Saalfeld. He led two infantry battalions in the Austrian victory at Neerwinden (18 March 1793), during which his battalions repulsed a strong French column. For his role at the head of his battalions of grenadiers, which his commander considered greater than duty required, in this victory, Merveldt received the honor of carrying the message to the Emperor Francis in Vienna. There, he was promoted to lieutenant colonel and awarded the Knight's Cross of the Military Order of Maria Theresa on 7 July 1794. Subsequently, he was appointed as an attaché to the staff of Frederick, Duke of York.
