The KKE was founded on 4 November 1918 by Aristos Arvanitis, Demosthenes Ligdopoulos, Stamatis Kokkinos, Michael Sideris, Nikos Dimitratos [el], and others.

Inspired by the Paris Commune and the communist revolutionary efforts in the United States, the German Empire, and Imperial Russia at the beginning of the century and the destruction that almost 20 years of wars had brought upon the Greek workers, a unified social-communist party was founded in Greece.

KKE and its organisations, although small in numbers, continue operating in all Greek major cities, especially industrial areas such as Athens, Piraeus, Patra, Thessaly and Volos, Thessaloniki, Kavala, and elsewhere.

KKE responded by creating the People's Front, which was the largest Marxist anti-fascist organisation in Greece prior to the dictatorship of Ioannis Metaxas.

The Security Police proved successful in dismantling the party structure; not only had it imprisoned the leadership, but it created a fake series of Rizospastis, the Central Committee newspaper.

[40] On the other hand, Woodhouse argues that Georgios Siantos, who had escaped from prison; and Nikos Zachariadis, who was still incarcerated, took the opposite view that KKE must support Metaxas in his fight against Mussolini.

[43][44] Nikos Zachariadis, KKE General Secretary, wrote from prison on 2 November 1940: "Today the Greek people are waging a war of national liberation against Mussolini's fascism.

According to KKE, the "Old Central Committee" based this opinion on the belief that Mussolini's Italy would not dare to attack a country that had a cooperation agreement with the Soviet Union.

[55] In any case, Zachariadis himself referred in his public statements after liberation almost exclusively to his first letter as proof of the patriotic character of KKE and its role as an inspiration to the Greek resistance movement during the war.

The pro-Nazi occupation government handed some of them over to the Nazis fearing that they—following the pro-Soviet party line—would resort to sabotage in Greece following Hitler's attack on the Soviet Union on 22 June 1941.

One of many stories includes the 20 communists held as political prisoners in Heraklion, Crete, who demanded to be released to fight against the invading Germans.

[64] Although the KKE was suffering from a lack of central political leadership since its leader Nikos Zachariadis had been taken by the Germans to the Dachau concentration camp, its members succeeded in maintaining communication with each other.

[66] In several other places and in major cities, small armed groups of KKE members and non-communists began to emerge, protecting people from looters, the Germans, or collaborators.

On 16 February 1942, the Greek People's Liberation Army (ELAS) was founded in a small kiosk in Phthiotis and by 1943 it consisted of 50,000 members, both men and women, with 30,000 as reserve units in major cities.

[68] ELAS conflicted finally with the rest of the resistance organizations and armies (especially EDES and EKKA), accusing most of them of being traitors and collaborators of the Nazis.

After several weeks, it became obvious to the KKE and EAM that the returning Greek government and their British allies were hostile to the significant amount of control that they exerted in Greece.

By mid-1946, these units forced the KKE leadership to change its neutral position and to plan the formation of a partisan army with the officers and fighters that were still free.

KKE's political influence and organization structure helped form units in the Aegean Islands of as Mytilene, Chios, Icaria, Samos and Crete.

The plan was for the Greek National Army to gain control of the border with Albania in order to surround and defeat the DSE forces, numbering 8,500 fighters.

On 28 August 1949, the Civil War in Greece ended with the DSE forces defeated militarily and politically and KKE entered a new phase in its history.

The crisis was already festering during the 12th plenum of the party's central committee held in Budapest between 5 and 15 February 1968 in which three members of the politbureau (M. Partsalidis, Z. Zografos and P. Dimitriu) were expelled for fractionist activity and was further triggered by the Soviet invasion of Czechoslovakia.

This event led a number of Greek communists who were ideologically leaning with the so-called opportunist faction to break with KKE that was loyal to the Socialist Republic's policy and to follow the nascent Eurocommunist line, which favored a more pluralistic approach to socialism.

In the June 1989 elections, Synaspismos gained 13.1 per cent of votes and joined a coalition with New Democracy to form a short-lived government amidst a political spectrum shaken by accusations of economic scandals against the previous administration of Andreas Papandreou's Panhellenic Socialist Movement.

In November of the same year, Synaspismos participated in the "Ecumenical government" with New Democracy and Panhellenic Socialist Movement which appointed Xenophon Zolotas as prime minister for three months.

Although KKE was again overtaken by PASOK (now called Movement for Change – KINAL) in the 2019 election, it nonetheless managed to maintain a fourth-place in the polls, due to the decline of far-right party Golden Dawn.

[96] In 2022, the KKE condemned "the imperialist war in Ukraine" by issuing an appeal, which was also signed by communist parties in Spain (PCTE), Turkey (TKP), and Mexico (PCM).

[97] The KKE has condemned Russia's actions, stating that "the murders of civilians is the most atrocious and barbarous picture of the imperialistic wars from whenever it comes from wherever they take place, either now in Ukraine due to the Russian invasion or in the past in Yugoslavia, Iraq, Syria and elsewhere with the responsibility of USA and NATO.

[100][101][102] In December 2015, KKE voted against the Civil Partnerships Bill proposed by Syriza that would extend cohabitation agreements to same-sex couples, responding, among other things: The family is a social relationship, it is an institution for the protection of children, as it was formed in the context of today's society, capitalism.

[103] However, the KKE also supports strengthening legislation to punish homophobic behavior, and has spoken against such discrimination, stating that "Unacceptable and condemnable discrimination and violence against our fellow human beings, based on their sexual orientation and other personal characteristics, are not addressed by cheap declarations of equality and words of sympathy, but by strengthening legislation against perpetrators of sexism, racism and homophobia, with the full social support of those who suffer from such behaviors.

Since its 18th congress (February 2009), KKE has opened up a discussion within the ranks and more broadly within the Greek left-leaning community on the future evolution of communism in the 21st century, with a particular emphasis on examining the causes of the collapse of the Socialist system in the former Soviet Union and in Eastern Europe.