Geyer followed his father in joining the Social Democratic Party of Germany (SPD), and studied history at university, receiving a doctorate in 1914.
He became a newspaper editor on various local SPD publications, but he opposed World War I and so joined the Independent Social Democratic Party of Germany (USPD), losing his job.
[1] Although Geyer lost influence in Leipzig to the right-wing of the USPD, he remained a national figure, and an early advocate of the Communist Party of Germany (KPD).
[1] In 1921, Geyer resigned from the KPD, in sympathy with Paul Levi, joining the Communist Working Group, then the USPD and the SPD.
There, he became sympathetic to the anti-German ideas of Robert Vansittart, joining the Fight for Freedom group, and being excluded from the Union of German Socialist Organisations in Great Britain.