In August 1916, when Romania entered World War I, Condeescu was made lieutenant-colonel. During much of the war, he did not command battle troops, instead working in military intelligence. He essentially built up this capacity of the Romanian Army from scratch, centralizing reports, studying the enemy armies, publishing orders and news bulletins, organizing espionage missions, identifying spies. The work eventually paid off with the victories at Mărăști and Mărășești, as the Romanian side was well informed about the position and plans of its adversaries. He also took measures to address the emerging threat of Soviet Russia.