The consultant's last day is on 15 May, having worked on government outreach for the agency's financial services clients, based in Brussels.
Reinhardt declined to comment on suggestions that he is launching his own agency, stating only that he would be staying in the world of financial services public affairs.
He is also a senior policy adviser at Fleishman-Hillard.
Reinhardt's expertise covers mergers and acquisitions, anti-cartel cases and corporate governance. He was formerly a merchant banker and securities trader for ABN Amro Bank.