[1] Julian Marchlewski was born in Włocławek, which was then under Russian rule, to a Polish Catholic father and a German Protestant mother, both of whom were of noble origin.

In 1896, he received a doctorate from Zurich University, after which he settled in Dresden, in Germany, where he and Alexander Parvus launched a newspaper, Sächsische Arbeiterzeitung, which they edited until they were both expelled from Saxony, in September 1898.

In December 1913, he launched a new journal, Sozialdemokratische Korrespondenz, using his flat as the editorial office, with himself, Rosa Luxemburg and Franz Mehring as the regular contributors.

[9] On the outbreak of war in 1914, he joined the small anti-war group within the SDP, led by Rosa Luxemburg and Karl Liebknecht, originally known as Gruppe Internationale, later as Spartakusbund, the forerunner of the German Communist Party.

After Liebknecht and Luxemburg had been murdered, in Berlin, he noticed that police were trailing him, and in disguise he joined a group of agricultural workers who were heading home to Galicia, which was now in Poland.

Returning to Moscow in June, he secured Lenin's support, but ran up against angry opposition from exiled leaders of the Polish communist party.

[11] In July 1920, during the Polish-Soviet War, Marchlewski was appointed Chairman of the Polish Provisional Revolutionary Committee (Tymczasowy Komitet Rewolucyjny Polski) in Białystok, implying that he would have been head of the Polish government had the Red Army won the war, though real power would probably have bene exercised by Dzerzhinsky, nominally his deputy.

Panzerregiment 23 "Julian Marchlewski", part of the 9th Panzer Division of the Land Forces of the National People's Army, was named in his honor.