He served as deputy chief of the Operations Staff, one of departments in the Oberkommando der Wehrmacht (OKW), the Armed Forces High Command.

In June 1914, just before the start of World War I, he was commissioned as a second lieutenant in the 10th Prussian Foot Artillery Regiment based in Alsace.

Reich War Minister Werner von Blomberg directed Warlimont to coordinate German aid in support of Franco's battle against the Spanish government forces.

In 1937, he wrote the Warlimont Memorandum calling for the reorganisation of the German armed forces under one staff unit and one supreme commander.

General Jodl was his superior officer, who served as Chief of the Operations Staff, which was responsible for all strategic, executive and war-operations planning.

During the Battle of France, on June 14, 1940, Warlimont, in an audacious move, asked the pilot of his personal Fieseler Storch to land on the Place de la Concorde in central Paris.

His meteoric advancement in rank almost sputtered out on 3 November 1942 when he was relieved of his job after a junior subordinate failed to process a message from Field Marshal Erwin Rommel sufficiently promptly.

However, only five days later he was recalled to duty to visit the French Vichy Government in France to coordinate the defense of their colonial territories from possible occupation by the Allies.

On 2 August, Warlimont met outside Paris with General Günther Blumentritt and advised him that Hitler wanted the Germans to regain the offensive initiative against the Allies through Operation Lüttich.

At Warlimont's request, due to his dizzy spells resulting from the 20 July assassination bombing against Hitler, he was transferred and retired to the OKH Command Pool (the Führerreserve), and was not further employed during the war.

He was convicted and sentenced to life imprisonment, in part for his responsibility for drafting the Barbarossa Jurisdiction Order which allowed the murder of civilians on the pretext of counteracting partisan activity.

This leniency was heavily criticized by Robert R. Bowie who stated: "they [Reinecke, Kuechler and Warlimont] were all directly implicated in the program which encompassed the murder of commandos, commissars and captured allied airmen as well as in brutal mistreatment of prisoners of war".