Born in Neuss, Herzfeld worked as a bank clerk in Düsseldorf, before moving to New York City, where he trained at the Columbia Law School.
[1] In 1887, Herzfeld joined the Social Democratic Party of Germany (SPD), and in 1898 he was elected to the Reichstag, representing Rostock.
He opposed World War I, joining the Social Democratic Working Group, and then becoming a founder of the Independent Social Democratic Party of Germany (USPD).
[1] Herzfeld remained a KPD member, devoting much of his time to the Rote Hilfe.
He emigrated to Switzerland in 1933, to escape Nazi persecution, and died there in 1939.