The 1st Army was activated on August 26, 1939 with General Erwin von Witzleben in command. Its primary mission was to guard the western defences of Germany against Allied forces along the Maginot Line, making it the principal adversary during the short-lived French Saar Offensive. During the battle of France, the army participated in the final breach of the line's defenses. After the French capitulation it spent until mid-1944 protecting the Atlantic coast of France from a possible seaborne incursion. Following the Normandy invasion in 1944, the army reorganized in Lorraine after a hasty retreat with the rest of the German forces across France in August 1944. During the battles along the German frontier, the First Army attempted to prevent the Third United States Army from crossing the Moselle River and capturing Metz while also attempting to hold the northern Vosges Mountains against the Seventh United States Army.
In November 1944, both defensive lines were broken and the First Army retreated to the German border and defended the Saarland of Germany, an important industrial region. With the Third U.S. Army engaged to the north against the German Ardennes Offensive, the 1st Army attacked the Seventh U.S. Army on New Year's Day 1945 in Operation Nordwind, causing the Americans to give ground and inflicting significant casualties where Seventh U.S. Army defensive lines were stretched taut by the length of frontage they had to cover. With the failure of Nordwind in late January, the 1st Army was first pushed back to the Siegfried Line and then forced to retreat across the Rhine River when the Allies pierced the German fortifications. Thereafter, the First Army made an ordered withdrawal to the Danube River before surrendering near the Alps on May 6, 1945.