The top Communist Party official in Ukraine during the 1932–33 famine, Chubar was posthumously held culpable for those events by a Ukrainian court in 2010.

Chubar returned to Ukraine in 1920, where he held a succession of economic posts, including running the Don basin coal combine in 1922–23.

In 1920, he objected to the appointment of a Russian, Vyacheslav Molotov, as secretary of the Ukrainian communist party, claiming that he knew very little about conditions in Ukraine.

In 1925, he objected to the appointment of Lazar Kaganovich who, like Molotov, was a trusted ally of Joseph Stalin, as First Secretary of the Ukrainian party.

[5] When their relations reached the breaking point in 1928 Stalin recalled Kaganovich, whose replacement, Stanisław Kosior, was much more acceptable to Chubar and other Ukrainian leaders.

Chubar became a candidate (non-voting) member of the Central Committee's Politburo in November 1926 – the first, and for many years the only ethnic Ukrainian to reach this level.

He was one of the speakers at a crucial session of the Central Committee in November 1929 who attacked Nikolai Bukharin and others who opposed forced collectivisation.

Kaganovich reported to Stalin that every member of the Politburo pleaded for a reduction in the quota of grain Ukraine was supposed to hand over, but he and Molotov "categorically refused".

[9] In December, Chubar had another clash with Kaganovich, who complained that fines imposed on peasants who failed to deliver their quota of grain were not being collected.

[14] Overruled, he signed an order that penalised three entire regions – Chernihiv, Kyiv and Vinnytsia – that were accused of "maliciously" failing to fulfill their quotas by prohibiting the sale of potatoes, which inevitably caused starvation, which the 2010 court verdict described as "murder by famine" of Ukrainian peasants.

[9] Assessing his role in Holodomor, the historian Robert Conquest wrote: "Chubar, who had expressed doubt, or rather certainty that Moscow's policies would lead to disaster, nevertheless enforced them.