Reinhardt was born on 24 March 1872 in Stuttgart as the son of August von Reinhardt (1827-1907), a member of the Personenadel (lifelong, non-hereditary nobility) and officer of the Kingdom of Württemberg (Generalmajor and Commander of the 120th Infantry Regiment), and Emilie Reinhardt, née von Wiedenmann. His brother Ernst (1870-1939) also became an officer (Generalleutnant) and was the father of Hellmuth Reinhardt (1900–89, Generalmajor). In 1900, Walther Reinhardt married Luise Fürbringer in Berlin. They had three daughters.