He spent his early adulthood in the service of the Emperor, winning laurels and titles for his efforts. After , Lallemand wandered the Western Hemisphere in search of the same adventure and sense of purpose that service in the French army had imparted.
In the twenty-five years running of his life after the fall of Napoleon, Lallemand travelled the Levant, attempted to plant a French colony in Spanish Texas, undertook the above invasion of Spain, and served as the military governor of Corsica. Lallemand's career has been described in both English- and French-language works. Contemporary encyclopedias offer further details. However, no biographical monograph exists in either English or French. The family produced another son in October , Henri-Dominique, who would follow his older brother into the military.
As an often-contested border province, the Lorraine produced a disproportionate percentage of France's military men; it is likely that Lallemand received at least rudimentary training in the military as part of his education. The coming of the Revolution brought opportunity for Lallemand. On 20 April , Revolutionary France declared war on the major powers of Europe. The government released a call for volunteers to fight the war. The French and Prussians met at Valmy on 20 September.
Lallemand's artillery company played a key role in the battle, which saw French citizen-soldiers standing firm against the professional soldiers of the most feared army in Europe. The war begun in sparked an international series of conflicts stretching over the next twenty-three years, providing opportunity for rapid advancement for men like Lallemand. In March , he transferred to the cavalry, which would remain his preferred service for the remainder of his career.
He continued acting as aide-de-camp to a variety of officers in Italy from to , where he fought in the decisive Battle of Rivoli on 14 January This relationship would prove important for Lallemand's career. He followed Junot through the ordeal of the Egyptian campaign, including attending negotiations between Junot and an English delegation led by Sir Sidney Smith.
