In 1898, Mankiewitz moved up to the management board of Deutsche Bank and, together with Oscar Wassermann, headed its stock exchange business in 1912.
He was a member of the supervisory board of Phönix AG für Bergbau und Hüttenbetrieb.
He set up financial aid that helped many students at German universities and technical institutes.
[5] Mankiewitz was a member of Deutsche Bank's management board for almost forty-five years.
His children fled Nazi Germany and survived, however, his wife's brother Richard was deported and killed in the Holocaust.