Velouchiotis was arrested for his communist ideas at the end of 1936 and jailed in Aegina, where he was tortured under the police interrogation techniques refined by Konstantinos Maniadakis, the Minister of Security.

There he presented himself as Major of Artillery (in hopes of gaining extra prestige among the villagers) with the nom de guerre of Aris Velouchiotis (from Ares, the Hellenic god of war, and Velouchi, a local mountain) and proclaimed the existence of the Greek People's Liberation Army (ELAS).

One of the most important early operations of the Greek resistance movement (in which Velouchiotis and his fighters, after negotiations with the British, agreed to participate alongside Napoleon Zervas's republican EDES resistance forces and twelve British saboteurs under the leadership of Major E. C. W. "Eddie" Myers) was the blowing-up of the Gorgopotamos railway viaduct, south of Lamia, on November 25, 1942 (Operation Harling).

The destruction of the viaduct cut the single Thessaloniki-Athens rail line, thus the line connecting the Balkans with southern Greece, but did not disrupt any supply lines—as would have been the case had it happened, as the British intended, two months earlier—to Erwin Rommel's German forces in Northern Africa, as it took place one month after the commencement of the El Alamein battle on October 23, 1942, in which Rommel was badly defeated by the British.

The rift ultimately led to a civil war in late 1943 and early 1944, in which ELAS attacked EDES, EOEA and destroyed EKKA's 5/42 Evzones Regiment, executing its leader Col. Dimitrios Psarros.

In October 1944, when the Nazis evacuated Greece, ELAS was the dominant force in most of the Greek cities, except Athens, while EAM had established its own government, the Political Committee of National Liberation (PEEA).

Velouchiotis moved again to the mountains of Central Greece in order to start an insurgency (see Greek Civil War) against the new government and the British allies who supported them.

He was reported to have denounced the sell-out to the British in the Varkiza Agreement to lay down the National Resistance arms; particularly moving was the sight of his elite massed Mavroskoufides (Black Berets) openly mourning.

Aris and his second in command, Giannis Aggeletos (nom de guerre: Leon Tzavellas), were isolated by the main unit, and finally, he committed suicide with his comrade, either by a hand grenade or by a bullet, on the same day he learned that he was denounced by the communist party.

[8] The corpses of Velouchiotis and Tzavellas were subsequently decapitated, and the heads displayed (a practice of the pre-war Greek State and Police for the common mountain bandits), hanging from a lamp post in the central square of the town of Trikala.

When British Labour government members of Parliament objected[citation needed] to the barbarity of the operation, they received the reply that the display was in accordance to an "ancient Greek war custom".

[citation needed] Following the rehabilitation in Greece of the EAM/ELAS and subsequently of the Communist party itself (after the end of the Greek military junta), busts and statues of Aris Velouchiotis have been erected in his native town.