Bernard Montalègre commanded the 27th Alpine Light Infantry Battalion, deployed in Upper Silesia from 1919 to 1922, before taking up garrison at Annecy in the summer of 1922. The battalion was part of the interposition troops of an international force, whose contingent was mainly French and made up the 46th Infantry Division. There were thus 2,600 Frenchmen at Gliwice. The mission was to ensure the security of the Inter-Allied Control Commission, to enforce and carry out the clauses of the peace treaty, and to ensure the fairness of the plebiscite scheduled for 20 March 1921. Indeed, the fate of Upper Silesia had not been settled by the Treaty of Versailles, and the region was contested by a reborn Poland and by Germany. The peace treaty therefore provided for a plebiscite, organised by an inter-allied commission, to decide the allegiance of this rich mining region according to the choice of the populations.
On 4 July 1921, in front of the officers' casino at Bytom, at the moment when the population was celebrating the entry of British troops into the town, Bernard Montalègre was killed by Leon Joschke, a German activist from Tarnowskie Góry. The site of the assassination is said to be today within the grounds of a surface-to-air artillery regiment, whose hall of honour contains mementos. The funeral took place at Gliwice on 8 July 1921, in the presence of a Polish government delegation and of French and British troops, among whom was Commander de Gaulle. On 27 July of the same year a solemn funeral mass was celebrated in Paris, with the participation of the French and Polish governments, of the Polish military mission and of a delegation from Upper Silesia, led by Wojciech Korfanty, the leader of the 3rd Silesian Uprising. A commemorative plaque was inaugurated at Bytom on 21 July 1978.