Weygand was the most junior of the PMRs (the others being the Italian Luigi Cadorna, the American Tasker H. Bliss, and the British Henry Wilson, later replaced by Henry Rawlinson). He was promoted général de division (equivalent to the Anglophone rank of major general) in 1918. This promotion was specifically because of his appointment as a PMR.
Weygand drew up the memorandum for the meeting of Foch with the national commanders-in-chief (Haig, Pétain and John J. Pershing) on 24 July 1918, the only such meeting before the autumn, in which Foch urged (successfully) the liberation of the Marne salient captured by the Germans in May (this offensive would become the Second Battle of the Marne, for which Foch was promoted Marshal of France), along with further offensives by the British and by the Americans at St Mihiel. Weygand personally delivered the directive for the Amiens attack to Haig. Foch and Weygand were shown around the liberated St. Mihiel sector by Pershing on 20 September.
Weygand later (in 1922) questioned whether Pétain's planned offensive by twenty-five divisions in Lorraine in November 1918 could have been supplied through a "zone of destruction" through which the Germans were retreating; his own and Foch's doubts about the feasibility of the plans were another factor in the seeking of an armistice. In 1918 Weygand served on the armistice negotiations, and it was Weygand who read out the armistice conditions to the Germans at Compiègne, in the railway carriage. He can be spotted in photographs of the armistice delegates, and also standing behind Foch's shoulder at Pétain's investiture as Marshal of France at the end of 1918.