He was a high-ranking member of the Socialist Unity Party of Germany . He was the successor to Erich Honecker as leader of East Germany from 18 October 1989 until 3 December 1989 , for a few weeks . He succeeded Erich Honecker as leader of the ruling Socialist Unity Party of Germany ( SED ) and head of state in October 1989 , but was ousted just under three months later amid the collapse of the communist regime .