Hardt was born in Graudenz, West Prussia (now Grudziądz, Poland).
He is the author of Priester des Todes (1898), Bunt ist das Leben (1902), An den Toren des Lebens (1904), and the plays Der Kampf ums Rosenrote (1903), Ninon von Lenclos (1905), Tantris der Narr (1907), Gudrun (1911), and Konig Salomo (1915).
He was director of the National Theater in Weimar (1919–24), the Schauspiel Köln in Cologne (1925), and the Westdeutscher Rundfunk (West German Broadcasting Co).
A few months later he was imprisoned for a short period and then took refuge in the Sankt Anna Hospital in Cologne-Lindenthal.
He was later acquitted in the "broadcast trial" and able, for a time, to resume some literary activities.