The Corps saw service throughout the entirety of World War I, notably participating in the Battle of Passchendaele (as part of the French First Army). At the time of the Battle of Passchendaele, the Corps comprised the 1st, 2nd, 51st and 162nd Infantry Divisions.
1st Army Corps was constituted on August 27, 1939, in Lille under the command of Major General Sciard as part of the French mobilization for war. Initially assigned as part of the French First Army, the corps was transferred to the French Seventh Army and moved to coastal regions near Calais and Dunkerque by mid-November 1939. On May 10, 1940, the Corps commanded the 25th Motorised Infantry Division (25e DIM) in addition to its organic units.
With the German invasion violating the neutrality of Belgium and the Netherlands on May 10, 1940, the 1st Army Corps moved into Belgium with the goal of gaining contact with the Dutch Army. This was achieved on May 12 near Breda, but the general failure of the Allies to hold the German advance mandated early retreats so that the 1st Army Corps would not be cut off. Breda fell to the Germans on May 13 and the corps conducted a fighting withdrawal through Dorp and Wuustwezel to the fortified zone of Antwerp, Belgium. During May 15–17, the corps defended the Scheldt Estuary with the 60th and 21st Infantry Divisions (60e DI and 21e DI), but was ordered to retreat back into France on May 18.
The period from May 19–26 saw the corps falling back to the line of the Somme River, where the French Army intended to make a major stand. Because of German advances, the 1st Army Corps had to deploy its divisional reconnaissance units to cover positions on the river that the slower-moving infantry divisions (4th Colonial Infantry Division - 4e DIC, 7th North African Infantry Division - 7e DINA, and the 19e DI) could then occupy. This required combat with the Germans, but the corps reached positions near Le Hamel, Aubigny, and along the road between Amiens and Saint-Quentin. During May 24–25, troops of the corps seized and lost Aubigny twice. The Germans, however, had held onto a large bridgehead at Peronne. The Germans broke out of this bridgehead on June 5, 1940, and continued their advance into the heart of France. A counterattack by armored elements of the corps on June 6 was halted by the Germans.
From June 9, the corps was involved in a succession of withdrawals that were meant to form lines of defense along the Avre, Oise, Nonette, Seine, and Loire rivers. The crossing of the Oise River was made under German air attack, some bridges were destroyed by the Luftwaffe, and portions of the corps' infantry had to surrender north of the Oise.