Studied chemistry in Braunschweig.
After his studies he took over his father's chemical factory and became a prosperous manufacturer. He fought at the front in an infantry regiment between 1914 and 1916, losing his left arm in combat and receiving the Iron Cross (First and Second Classes).
In December 1918 he founded (together with Theodor Duesterberg) the Stahlhelm, a nationalist veterans’ organization which was to become the largest para-military group in Weimar Germany, along with the National Socialist storm troopers. Seldte called on ex-servicemen to fight against ‘the slavery of the Versailles Diktat’, demanded ‘adequate lebensraum' for Germany and decried Marxist internationalism and pacifism as enemies of the nation. Under his leadership, the Stahlhelm aided and abetted the Nazi rise to power - in spite of some organizational rivalries - by consistently undermining the stability of the Weimar Republic.
Following Hitler’s appointment as Chancellor, Seldte became Reich Minister of Labour, a position he held until the collapse of Nazi Germany. Labour Minister for Prussia, a Prussian State Councillor, member of the Reichstag and, from March 1934, leader of the ‘co-ordinated' National Socialist German Veterans' Organization, Seldte presided without demur over the dissolution of the Stahlhelm and faithfully served the Third Reich.
He died in Fiirth, Bavaria, on 1 April 1947.