Malaya, then under British administration, was gradually occupied by Japanese forces between 8 December 1941 and the Allied surrender at Singapore on 15 February 1942. The Japanese remained in occupation until their surrender to the Allies in 1945. The first Japanese garrison in Malaya to lay down their arms was in Penang on 2 September 1945 aboard HMS Nelson.

The concept of a unified East Asia took form based on an Imperial Japanese Army concept that originated with Hachirō Arita, who served as Minister for Foreign Affairs from 1936 to 1940. The Japanese Army said the new Japanese empire was an Asian equivalent of the Monroe Doctrine, especially with the Roosevelt Corollary. The regions of Asia, it was argued, were as essential to Japan as Latin America was to the U.S.

The Japanese Foreign Minister Yōsuke Matsuoka formally announced the idea of the Co-Prosperity Sphere on 1 August 1940, in a press interview, but it had existed in other forms for many years. Leaders in Japan had long had an interest in the idea. The outbreak of World War II fighting in Europe had given the Japanese an opportunity to demand the withdrawal of support from China in the name of "Asia for Asiatics", with the European powers unable to effectively retaliate. Many of the other nations within the boundaries of the sphere were under colonial rule and elements of their population were sympathetic to Japan (as in the case of Indonesia), occupied by Japan in the early phases of the war and reformed under puppet governments, or already under Japan's control at the outset (as in the case of Manchukuo). These factors helped make the formation of the sphere while lacking any real authority or joint power, come together without much difficulty. The sphere would, according to imperial propaganda, establish a new international order seeking "co prosperity" for Asian countries which would share prosperity and peace, free from Western colonialism and domination under the umbrella of a benevolent Japan. ธิชาภัทร สมใจ(1987)

Japanese Military Affairs Bureau Unit 82 was formed in 1939 or 1940 and based in Taiwan to bring this about. In its final planning stages, the unit was under the then-Colonel Yoshihide Hayashi. Intelligence on Malaya was gathered through a network of agents which included Japanese embassy staff; disaffected Malayans (particularly members of the Japanese established Tortoise Society); and Japanese, Korean, and Taiwanese business people and tourists. Japanese spies, which included a British intelligence officer, Captain Patrick Stanley Vaughan Heenan and Lord Sempill also provided intelligence and assistance. Heenan's intelligence enabled the Japanese to destroy much of the Allied air forces on the ground.

Prior to hostilities, Japanese intelligence officers like Iwaichi Fujiwara had established covert intelligence offices (or Kikans) that linked up with the Malay and Indian pro-independence organisations such as Kesatuan Melayu Muda in Malaya and the Indian Independence League. The Japanese gave these movements financial support in return for their members providing intelligence and later assistance in determining Allied troop movements, strengths, and dispositions prior to the invasion.

By 1941 the Japanese had been engaged for four years in trying to subjugate China. They were heavily reliant on imported materials for their military forces, particularly oil from the United States. From 1940 to 1941, the United States, the United Kingdom, and the Netherlands imposed embargoes on supplying oil and war materials to Japan. The object of the embargoes was to assist the Chinese and encourage the Japanese to halt military action in China. The Japanese considered that pulling out of China would result in a loss of face and decided instead to take military action against US, British and Dutch territories in South East Asia. The Japanese forces for the invasion were assembled in 1941 on Hainan Island and in French Indochina. The troop build-up in Indo-China and Hainan was noticed by the Allies and, when asked, the Japanese advised that it related to its operations in China.

The occupation commenced with Imperial Japanese Army landings at Padang Pak Amat beach Kota Bharu just after midnight on 8 December 1941, triggering a ferocious battle with the British Indian Army an hour before the attack on Pearl Harbor. This battle marked the official start of the Pacific War and the start of the Japanese occupation of Malaya. Kota Bharu airport was occupied in the morning. Sungai Patani, Butterworth, and Alor Star airports were captured on 9 December 1941. Japanese soldiers landing at Kota Bharu divided into two separate forces, with one moving down the east coast towards Kuantan, and the other southwards towards the Perak River. On 11 December 1941, the Japanese started bombing Penang. Jitra and then Alor Star fell into Japanese hands on 12 December 1941. The British had to retreat to the south. On 16 December 1941, the British left Penang to the Japanese, who occupied it on 19 December.

The Japanese continued to advance southwards, capturing Ipoh on 26 December. Fierce resistance to Japanese progress in the Battle of Kampar lasted three days and three nights between 30 December 1941 and 2 January 1942, before the British had to retreat once again. On 7 January 1942, two brigades of the 11th Indian Infantry Division were defeated in the Battle of Slim River, giving the Japanese army easy passage to Kuala Lumpur, the capital of Malaya. On 9 January, the British position was becoming more desperate and the ABDACOM Supreme Commander, General Wavell, decided to withdraw all the British and Commonwealth forces south to Johor, thus abandoning Kuala Lumpur (which was captured by the Japanese on 13 January).