He emigrated to the Soviet Union in 1939, days before the Invasion of Poland, where he was active in the fight against the Nazi state as editor-in-chief of the newspaper Freies Deutschland in the National Committee for a Free Germany from 1944 during the German-Soviet War.

In the early 1950s, Herrnstadt campaigned for democratization within the SED, but lost the power struggle against the General Secretary of the Central Committee, Walter Ulbricht.

After the uprising of 17 June 1953, where Herrnstadt had shown understanding for the protests in articles in Neues Deutschland, he and other opponents of Ulbricht lost their seat on the Central Committee for "forming anti-party factions."

[3] While exiled in Moscow, Herrnstadt met Valentina Veloyants (Валентина Велоянца), a scholar of Germany and together had a child Irina Liebmann who would go on to be journalist and well known author as well as a sinologist of Russo-German provenance.

[3] He earned his living from support payments from his parents and as an editor for the Drei-Masken publishing house, while at the same time working as a freelance writer.

However, in November 1929, Herrnstadt was sacked by the Rudolf Mosse publishing company for writing a sensationalist story about 240,000 workers in the Ruhr region who had been locked out of work.

[15] His persistence brought him to the notice of Soviet military intelligence, who recruited him as a Red Army GRU agent[15] and gave him the codename "Arbin".

[19] In Germany, the arrival of Adolf Hitler at the seat of power would have made Herrnstadt a target, both as an unrepentant communist activist and as a Jew.

By 1936, these included folk from the Germany embassy that included the ambassador Hans-Adolf von Moltke, the legation councillor Rudolf von Scheliha and the press-secretary Hans Graf Huyn [de],[20] as well as connections to the Polish writer Jarosław Iwaszkiewicz, poet Julian Tuwim, the actress Ida Kaminska and the Polish foreign minister Josef Beck.

[19] Herrnstadt's espionage group in Warsaw was made up of him and Stöbe and included Gerhard Kegel [de] and his wife Charlotte Vogt, the couple Marta (Margarita) and lawyer Kurt Welkisch [ru], at times also the publisher Helmut Kindler [de] and his childhood friend, the lawyer Lothar Bolz.

[22] After the German-Polish non-aggression pact concluded in 1934, Herrnstadt "turned his attention entirely to efforts to create a security alliance between Poland and Hitler's Germany.

"[23] By 1936, using the Editor's Law, the Reich Ministry of Public Enlightenment and Propaganda had removed many foreign Jewish correspondents and by that point only a few remained.

[28] To convince him otherwise, Herrnstadt decided to persuade Von Scheliha to pass embassy reports by disguising the delivery location of the intelligence, i.e. to show they weren't going to the Soviet Union.

[b][30] When he returned to Warsaw, he informed Von Scheliha that had met a contact in England, who was an "intermediary" for the secret service who was interested in the political situation in Poland.

[35] According to a report by German political author and historian Wolfgang Leonhard, his "upper-class past" was evident, among other things, from the fact that while he was still working in the Soviet Union as chief editor of the Freies Deutschland newspaper, he attracted attention by addressing his subordinates using the formal "You".

[36] When the Moscow-based KPD leadership established a special commission to prepare for the defeat and return to Germany, Herrnstadt was one of the committee members.

[39] In August 1945, Herrnstaft founded the general Allgemeiner Deutscher Verlag publishing house with himself, Kegel and Friedrich Notz as managing directors.

[43] Although Herrnstadt was defending Russian forces, for the first time, the barabarism of the Red Army was openly discussed, in effect breaking the official silence on the subject, which was considered taboo, even under occupation law.

[35] After the death of Joseph Stalin on 5 March 1953, on 2 June, the Soviet Union ordered the SED to adopt the New Course, which was intended to reverse or slow down the construction of socialism in the GDR that had been pushed forward since 1952.

When he complained to the new Soviet High Commissioner Vladimir Semyonov about the speed of the ordered change of course, the latter replied: "In 14 days you may no longer have a state.

"[49][50] On the 9 June, within the Politburo, Herrnstadt now positioned himself together with the Minister for State Security Wilhelm Zaisser and leading party ideologist, as an opponent of Ulbricht.

On 14 June 1953, Herrnstadt published a report in Neues Deutschland under the title "It's time to put the sledgehammer aside" (Den Holzhammer beiseite legen).

The authors critically examined the dictatorial methods used by the SED to decide on the increase in work standards at the VEB Wohnungsbau [de] and to announce this for 30 June.

[51] Even if the article did not demand the withdrawal of the increase in standards, it nevertheless acted as a beacon, as it showed that the policies of the Central Committee General Secretary Walter Ulbricht were controversial even within the inner circles of power in the SED.

The Soviet ambassador in East Berlin, Ivan Ilyichov, asked him to join Zaisser in calling on Ulbricht to step down from power: "He is a sensible man, he will understand that.

Wilfried Loth, on the other hand, saw the declaration as an indication that the Soviet Union "did not want the GDR" and - as in the Stalin notes of 1952 - would have preferred a neutral, democratic, united Germany.

[55] However, because the increase in standards was not withdrawn, the New Course was no longer able to stop the 1953 East German Uprising of 17 June 1953, which initially weakened Ulbricht's position in the SED and the Soviet Union.

Zaisser, Friedrich Ebert Jr., Heinrich Rau and Elli Schmidt agreed with him; only Matern and Erich Honecker spoke in favor of Ulbricht.

He presented the New Course as the cause of the “fascist putsch” (the official GDR term for the uprising of 17 June 1953) and attacked Herrnstadt, whom he accused of “directly supporting the strikers”.

"[49] After the plenary session, a journalistic campaign orchestrated by Ulbricht's collaborator Karl Schirdewan began against Herrnstadt and Zaisser, who were publicly described as “Trotskyists” and “enemies of the German people and the party of the working class”.