[1] He joined the Social Democracy of the Kingdom of Poland and Lithuania (SDKPiL), led by Rosa Luxemburg and Jan Tyszka in Warsaw, in July 1904.

In 1911, Domski supported the rozlamovist, group, led by Yakov Hanecki and Karl Radek, who objected to Jan Tyszka's leadership style.

Domski first emerged as a critic of the official line in July 1920, during the Polish–Soviet War, when he called on the soviet government to abandon the idea of using the Red Army to bring Poland under communist rule, and welcomed a report that peace negotiations might be in prospect.

Writing in the German communist newspaper Rote Fahne, he argued: "Soviet Russia's struggle against Polish reaction is not merely military, but rather has a political aim: erecting the dictatorship of the proletariat in Poland.

[6] In February 1924, Domski, Julian Lenski and two others, all based in exile in Berlin, co-signed a document calling on the Polish communist party to develop a 'Bolshevik backbone'.

[7]Joseph Stalin and Grigory Zinoviev, the chairman of Comintern, who was tightening control over Europe's communist parties, gave his backing to the Berlin Four, despite having criticised Domski in the past as an ultra-leftist.

In July 1925, a commission chaired by Stalin accused Domski of a series of errors dating back to his criticism of the war with Poland five years earlier.