He is best known for regrouping the retreating allied armies to defeat the Germans at the strategically decisive First Battle of the Marne in September 1914.
His political position waned after unsuccessful offensives in 1915, the German attack on Verdun in 1916, and the disappointing results of the Anglo-French offensive on the Somme in 1916.
At the end of 1916 he was promoted to Marshal of France, the first such promotion under the Third Republic, and moved to an advisory role, from which he quickly resigned.
Later in the war he led an important mission to the United States.
His popularity led to his nickname Papa Joffre.