Under Liggett's leadership, the I Corps participated in the Second Battle of the Marne and in the reduction of the Saint-Mihiel salient. In October 1918, as commander of the First United States Army with the rank of lieutenant general in the national army, he directed the final phases of the Meuse-Argonne offensive and the pursuit of German forces until the armistice. After commanding the post-war Army of Occupation, Liggett returned to his permanent rank of major general, and retired in 1921.