Allied commander Dwight D. Eisenhower struck a controversial deal with Darlan, recognizing him as High Commissioner of France for North and West Africa.

In 1936, he went to London on an unsuccessful mission to persuade the Admiralty that greater Anglo-French naval co-operation was needed given the way that Germany and Italy had aligned as a result of the Spanish Civil War.

[6] Blum stated that Darlan "thinks exactly as I do" about a potential Italian naval threat to France, and selected him as the next chief of staff of the Marine to replace the pro-Italian Admiral Georges Durand-Viel.

[4] Through Blum did not take up Darlan's suggestion, he did approve of him as an admiral with strong anti-Italian views, which he considered to be a refreshing contrast to Durand-Viel who advocated a Franco-Italian alliance.

The American historian Reynolds Salerno wrote: "While Durand-Viel was a soft-spoken, cautious administrator who sought out advice from his subordinates and deferred to his minister for major policy decisions, Darlan was an extremely self-confident, resolute admiral who monopolized every aspect of the Marine".

[7] Salerno described Darlan as a conservative French nationalist who was committed to preserving France as a great power via a programe of building more warships for the Marine.

[9] In 1939 he was promoted to Amiral de la flotte, a rank created specifically to put him on equal terms with the First Sea Lord of the Royal Navy.

[14] The acute crisis in Franco-Italian relations in the winter of 1938-1939 served to reinforce Darlan's arguments within the French government for an offensive strategy against Italy..[14] At a meeting of the defense chiefs in January 1939, Darlan stated in the event of a war the Marine should sever the sea-lanes linking Italy to its colony of Libya while French warships should bombard Naples, La Spezia, and Pantelleria.

[15] It was agreed at the Darlan-Pound meeting that the French fleet should remain focused on the Mediterranean with the majority of the French fleet to be stationed at the naval bases at Toulon, Mers El Kébir and Bizerte with only one squadron to be based at Brest on France's Atlantic coast as the Royal Navy was to take responsibility for the rest of the North Atlantic and the North Sea.

[16] At a meeting of the Anglo-French Supreme War Council on 22 September 1939, Darlan sided with the British in opposing Daladier's plans to take the Armée du Levant from Beirut to Thessaloniki with the aim of opening a second front in the Balkans as a way to aid Poland.

[16] Initially, Darlan had supported the British who believed that a naval blockade along with strategical bombing would be sufficient to defeat the Reich without any major land battles.

[17] In particular, Darlan noted that because of the Molotov-Ribbentrop pact that Germany had access to all of the vast natural resources of the Soviet Union, which rendered the Anglo-French naval blockade rather ineffectual.

[17] The Soviet Union was self-sufficient in virtually all of the natural resources needed to sustain a modern industrial economy, and German-Soviet trade defeated the purposes of the naval blockade.

[20] Darlan was one of the main advocates of a Scandinavian expedition, arguing to seize the Swedish iron mines would cause collapse of the German economy no later than the spring of 1941.

[23] The plans for a Scandinavian expedition drew strong opposition from Maurice Gamelin who argued that best place for French manpower was in defending France from the expected German invasion.

[27] Darlan was immensely proud of the French navy which he had helped to build up, and after Axis forces defeated France (May–June 1940), on 3 June he threatened that he would mutiny and lead the fleet to fight under the British flag in the event of an armistice.

[31] On 16 June Churchill's telegram arrived agreeing to an armistice (France and Britain were bound by treaty not to seek a separate peace) provided the French fleet was moved to British ports.

[32] That day, according to Jules Moch, he declared that Britain was finished so there was no point in continuing to fight, and he was concerned that if there was no armistice Hitler would invade French North Africa via Franco's Spain.

[28] That evening Paul Reynaud, feeling he lacked sufficient cabinet support for continuing the war, resigned as Prime Minister, and Philippe Pétain formed a new government with a view to seeking an armistice with Germany.

[29]: 139–40  On 18 June Darlan gave his "word of honour" to the British First Sea Lord, Sir Dudley Pound that he would not allow the French fleet to fall into German hands.

[33] Darlan ordered all ships then in the Atlantic ports (which Germany would soon occupy) to steam to French overseas possessions, out of reach of the Germans, although not necessarily of the Italians.

The British lacked confidence that Darlan was being straight with them (one government adviser minuted that he had 'turned crook like the rest')[29]: 149  and believed that, even if he was sincere, he could not deliver on his promise.

[37] After Allied forces captured French Syria and Lebanon in June–July 1941, and the German invasion of the USSR stalled before Moscow by December 1941, Darlan moved away from his policy of collaboration.

[36] An elaborate conspiracy theory, the Pacte Synarchique, was devised by more pro-German elements in the Vichy regime to discredit Laval and his technocratic circle arguing that a group of financiers aimed for French defeat in the Battle of France but also plotted against the National Revolution.

They prepared with Henri d'Astier de la Vigerie to support the expected Allied landings and met with General Mark Clark in Vichy Morocco, who provided them with weapons.

The Allies had anticipated little response from French forces in North Africa, and instead expected them to accept the authority of General Henri Giraud, sent from France to take charge.

To bring a quick end to the resistance and secure French co-operation, the Allies put a lot of pressure on Darlan, who released a general cease-fire (including Morocco) after two days (on 10 November).

Eisenhower's recognition of Darlan was right, he said, and even if not quite right, it meant French rifles pointed not at Allies, but at Axis soldiers: "I am sorry to have to mention a point like this, but it makes a lot of difference to a soldier whether a man fires his gun at him, or at an enemy..."[45]: 275  At the time, Churchill saw Darlan rather than de Gaulle as the better French ally, saying in the same speech that "de Gaulle is no unfaltering friend of Britain".

[37] American historian Robert Paxton on the contrary considers it is a thesis "based on too many post-war pleas to be credible":[47] archives showing Darlan making every effort to discourage and then thwart Allied action.

[50] Darlan refused to repeal the most aggressive laws and measures of the Vichy regime, which resulted in political prisoners remaining in concentration camps of the South.