He eventually entered the military service of the Habsburg Monarchy in 1793. Ficquelmont participated in all Austrian campaigns in the Revolutionary and Napoleonic Wars and was regarded as a brilliant military officer. In 1809, he rose to the rank of Oberst and was appointed chief of staff of Archduke Ferdinand Karl Joseph of Austria-Este. In 1811 and 1812, he led troops in Spain, where his victories attracted the attention of Emperor Napoleon I, who unsuccessfully tried to recruit him. He was then elevated to the rank of Generalmajor in 1814 and received the capitulation of Lyon a few months later.