[2][3] When the Nazis took power in Germany in 1933, Eberlein fled to the Soviet Union, where he found refuge at the Hotel Lux.

In the KPD in the 1920s, Eberlein, who was also a member of the Prussian state parliament from 1921 to 1933, initially supported the party leadership around Heinrich Brandler and August Thalheimer, then belonged to the so-called middle group, and from 1927 was part of the conciliators, who were driven out of the KPD's leadership in 1929 after the Wittorf affair and the return of Ernst Thälmann to power at the direction of Joseph Stalin.

From that point he was employed, like Arthur Ewert and Kurt Sauerland, under the leadership of Béla Kun in the apparatus of the Comintern.

After being briefly imprisoned after the National Socialists seized power in 1933, Eberlein was able to go into exile in France, where he campaigned for the establishment of a popular front between communists, social democrats and bourgeois forces.

On May 5, 1939, at a closed session of the Military Collegium of the USSR Supreme Court, he was sentenced to 15 years in the gulag for allegedly being involved in a "terrorist organization" within the Comintern apparatus as part of the "anti-Comintern bloc".

Hugo Eberlein is also commemorated on the tombstone of his son Werner in the graves for victims of fascism and those persecuted by the Nazi regime in Berlin's Friedrichsfelde Central Cemetery.