Jacob experienced the First World War whilst serving on the western front in 1918. This led him to become a pacifist. He went on to become a radical critic of German militarism writing articles about German secret rearmament and the Feme murders. From 1923 he wrote a series of articles for Die Weltbühne under the pseudonym "Old Soldier". However, in 1928 he was prosecuted for treason and sentenced to nine months imprisonment.
Jacob left Germany for Strasbourg 1932. Here he set up an independent press service. However having been enticed to Basle by the undercover Gestapo agent Hans Wesemann, Jacob was kidnapped in March 1935. Jacob had known Wesemann for some time and had indeed served as best man at Wesemann's wedding. Wesemann was subsequently sentenced to three years in jail for the kidnapping. This was investigated by the Swiss police officer Anton Ganz, who went to London to interview such people as Dora Fabian and Karl Korsch. The subsequent death of Fabian alongside her friend Mathilde Wurm led to concern that they had been murdered rather than the suicide which was the verdict of the coroner's court. This contributed to the climate of opinion which led to a successful campaign for his release from Germany. This campaign was based on Swiss diplomatic pressure and German exile protests.
Upon his return to Switzerland he was deported to France. Here he continued his work until the outbreak of the Second world War. He was interned with his wife in the south of France in 1939/40. However they managed to escape from Marseille travelling to Portugal in 1941. Jacob was one of the refugees aided by Varian Fry. However Jacob was once again kidnapped in Lisbon by the nazis and held in the Gestapo prison at Prinz Albrecht Strasse, Berlin. Owing to the harsh treatment he endured Berthold Jacob died in the Berlin Jewish Hospital on February 26, 1944.
- 1925: Weissbuch über die Schwarze Reichswehr (with Emil Julius Gumbel) Berlin: Verlag der Neuen Gesellschaft,
- 1925: Deutschlands geheime Rüstungen? Berlin: Verlag der Neuen Gesellschaft
- 1929: Verräter verfallen der Feme: Opfer, Mörder, Richter 1919–1929 (with Emil Julius Gumbel, Ernst Falck) Berlin: Malik
- 1934: Die Hindenburg-Legende. Verlag La République, Strasbourg
- 1934: Wer? Aus dem Arsenal der Reichstagsbrandstifter. Strasbourg
- 1934: Memoiren des Stabschefs Röhm. (Anonymous) Strasbourg
- 1936: Das neue deutsche Heer und seine Führer: Mit einer Rangliste des deutschen Heeres und Dienstaltersliste (nach dem Stande von Mitte August 1936).
- 1936: Warum schweigt die Welt? (with contributions from Carl von Ossietzky, Georg Bernhard, Wolf Franck, Jack Iwo, Alfred Kantorowicz, Rudolf Leonhard, Paul Westheim) Paris: Éditions du Phénix
- 1937: Weltbürger Ossietzky. Ein Abriss seines Werkes (with a biography of Ossietzkys, and foreword by Wickham Steed) Paris: Éditions du Carrefour
- "German Resistance Memorial Center - Biographie". www.gdw-berlin.de. Gedenkstätte Deutscher Widerstand. Retrieved 31 December 2017.
- "Annual 3 Chapter 4-Simon Wiesenthal Center Multimedia Learning Center". motlc.wiesenthal.com. The Simon Wiesenthal Center. Retrieved 31 December 2017.
- "Wesemann, Nazi agent, sentenced to three years for kidnapping Berthold Jacob". Europeana Collections. Retrieved 31 December 2017.
- Brinson, Charmian (1992). "The Strange Case of Dora Fabian and Mathilde Wurm". German Life and Letters. $5:4 (October 1992).
- "Some of the 2,000 people assisted by Varian Fry and the Emergency Rescue Committee." Varian Fry Institute, February 12, 2008. Accessed 31 December 2017.