After World War II, the party was legalized in 1945 by the Allied occupation authorities, but its unexpected success in the 1949 general election led to the "Red Purge", in which tens of thousands of actual and suspected communists were fired from their jobs in government, education, and industry.

The Soviet Union encouraged the JCP to respond with a violent revolution, and the resulting internal debate fractured the party into several factions.

The dominant faction, backed by the Soviets, waged an unsuccessful guerrilla campaign in rural areas, which undercut the party's public support.

The party maintained a neutral stance during the Sino-Soviet split, declared its support for multi-party democracy in opposition to the one-party politics of China and the Soviet Union, and purged pro-Soviet or Chinese members.

His efforts to regain electoral support were particularly successful in urban areas such as Osaka, Kyoto, and Tokyo, and the JCP worked with the Japan Socialist Party (JSP) in the 1970s to elect a number of progressive mayors and governors.

It believes that this objective can be achieved by working within an electoral framework while carrying out an extra-parliamentary struggle against "imperialism and its subordinate ally, monopoly capital".

A staunchly anti-militarist party, the JCP firmly supports Article 9 of the Japanese Constitution and seeks to dissolve the Japan Self-Defense Forces.

The three former anarchists were reluctant to found the JCP, with Yamakawa shortly after arguing that Japan was not ready for a communist party and calling for work to be done solely within labor unions.

Sano, Watanabe, Shoichi Ichikawa, Kenzō Yamamoto, and Hideo Namba avoided arrest as they were serving as representatives to the 6th World Congress of the Communist International and reorganized the party.

An attempt to reform Hyōgikai resulted in arrests so a new organization, the National Council of Japanese Labor Unions (Zenkyō), was formed as an underground group with 5,500 members on 25 December 1928.

The first issue of Shimbun Akahata after the end of the war thanked the Allied occupation for the "democratic revolution" that was occurring and called for the recreation of a communist political party.

[32] According to Jacobin, the JCP, unlike the French, and Italian communists, emerged into the postwar period without an organizational base established through wartime resistance movements.

[35] Nosaka's strategy involved avoiding open calls for violent revolution and taking advantage of the seemingly pro-labor stance of the Allied occupation to organize the urban working classes and win power at the ballot box and through propaganda.

[38] Beginning in the fall of 1949, in reaction to the JCP's electoral success and as part of the "Reverse Course" in Allied occupation policy amid rising Cold War tensions, the Allied occupation authorities and the Japanese government carried out a sweeping Red Purge, firing tens of thousands of communists and suspected communists from government posts, teaching positions at schools, and private corporations.

[42] Against this backdrop in January 1950, the Soviet-led Cominform, at the behest of Soviet premier Joseph Stalin, issued a blistering criticism of the JCP's peaceful line as "opportunism" and "glorifying American imperialism".

Militants were rounded up, tried, and sentenced to lengthy prison terms, and in the 1952 general election, Japanese voters vented their ire at the JCP by stripping the party of every single one of its 35 Diet seats, a blow from which it would take two decades to recover.

[51] The JCP took a different line than the Japan Socialist Party, Sohyo labor federation, and other groups who argued that the main target of the protest movement was Japanese monopoly capitalism.

[60] In the 1972 general election, the JCP won an astonishing 38 seats in the Diet, surpassing its 1949 high of 35 and signaling the party's full recovery from the disastrous militant line of the early 1950s.

[58] After the dissolution of the Soviet Union, the JCP released a press statement titled "We welcome the end of a party which embodied the historical evil of great power chauvinism and hegemonism".

[citation needed] In September 2015, after the passage of the 2015 Japanese military legislation, the JCP called for cooperation from other opposition parties to form an interim government to abolish the bills.

[62] The JCP has stated that it supports the establishment of a democratic republic, but also that "[the monarchy's] continuation or discontinuation should be decided by the will of the majority of the people in future, when the time is ripe to do so".

[93] The JCP has been one of the political parties to vocally back LGBTQ+ rights in the country; communist lawmakers have been working to win the passage of same-sex marriage and anti-discrimination laws in parliament.

[95] The JCP has maintained a friendly relationship with the Japanese feminist camp since its inception, and is still the most active in women's rights issues among Japan's major political parties.

The JCP advocates that Japan issue further apologies for its actions during World War II and has condemned prime ministerial visits to Yasukuni Shrine.

[113] The JCP opposes the possession of nuclear weapons by any country, military blocs, and attempts to revise Article 9 of the Japanese Constitution, which says that "never again ... [will Japan] be visited with the horrors of war through the action of government".

At the same time, the party had distanced itself from Mao and Maoism, which allowed it to avoid being associated with China's Great Leap Forward and Cultural Revolution once they started coming more fully to light in the 1970s.

In July 1969, the JCP declared that if it ever came to power, it would permit the free functioning of opposition parties, in an effort to distinguish itself from the one-party states in the Soviet Union and China.

The new platform criticized the Chinese Communist Party, denouncing China's "great-power chauvinism and hegemonism" as "an adverse current to world peace and progress".

The party constitutions states decisions "shall be based on democratic discussion and finally decided by majority vote" and that "there shall be no factions or splinter groups".

The group was founded in Kyoto in 2011 and is directed by Tadao Yamamoto, a composer, accordionist, choir director, and ordinary member of the National Council of The Singing Voice of Japan.