In 1899, he relocated with his mother and sister to Berlin, where he attended school (Gymnasium) and thereupon completed studies in piano at a conservatory.

Upon resuming his studies, he befriended Paul Levi and Ruth Fischer, who convinced him to join the Communist Party of Germany (KPD).

Taken into custody by the Berlin police in 1922, he identified himself as a Soviet agent and a confidant of Leon Trotsky and Karl Radek.

In April 1924, Maslow and Fischer, criticized as “right-wing” by August Thalheimer and Heinrich Brandler, assumed leadership of the Party and were responsible for intensifying the “left-turn” of the KPD.

Taken once again into custody in May 1925, Maslow, together with Paul Schlecht and Anton Grylewicz, was brought to court and sentenced to four years in prison.

Since Maslow and Fischer no longer enjoyed the protection of Grigory Zinoviev, under a directive of Joseph Stalin to favor Ernst Thälmann, they were relieved of the Party leadership, and on August 20, 1926, were excluded from the KPD.

Together with Ruth Fischer and Hugo Urbahns, Maslow brought together former members of the left wing of the KPD, which led to formation of the Leninbund in early 1928.