Hammerstein-Equord was born to a noble family, which had already produced several famous officers, in Hinrichshagen, Mecklenburg-Strelitz, German Empire in 1878. His parents were the head forester ("Oberförster") of the Grand Duchy of Mecklenburg-Strelitz, Heino von Hammerstein, and his wife Ida, née Gustedt (also from a noble family). After initial schooling Hammerstein-Equord joined the Cadet Corps in Plön in 1888 at the age of ten, followed by the Prussian Cadet Corps Berlin-Lichterfelde in 1893. He officially entered the German army on 15 March 1898 upon his promotion to lieutenant ("Secondelieutenant") while serving with the 3rd Foot Guards.