He had been a director of NYSE Euronext since April 2007 until December 2009.
Before he resigned, he had been the chief executive officer and chairman of the managing board of Euronext since its creation in September 2000. 
He was the architect of the takeover that united Euronext, Europe’s second-largest exchange with the New York Stock Exchange. He became head of the French bourse in 1990 and is regarded as a pioneer of consolidation among exchanges. He brokered an alliance of markets in Amsterdam, Paris and Brussels to create Euronext in September 2000 and then orchestrated an initial public offering of the company the next year. In 2001, he beat rivals Deutsche Boerse AG and London Stock Exchange Group Plc. to acquire Liffe.
Theodore began his career with the French Treasury (Direction du Tresor) at the Ministry of Economy and Finance from 1974 to 1990, serving as assistant head of the State Holdings Bureau. He was then seconded for two years to Credit National. On his return to the Treasury, he was appointed head of the 'African States' Franc Zone' Bureau, and then head of the Foreign Investment Bureau. In 1984, he was appointed deputy director in charge of the Banking Department; in 1986, he was appointed deputy director in charge of the Investments, Public Corporations Department, and in 1990, he became chief executive officer of ParisBourse SBF S.A. He presided over the International Federation of Stock Exchanges (FIBV) for two years (1993-1994), and served as president of the Federation of European Stock Exchanges (1998-2000).
From 1993 to 2000, he was the chairman of SICOVAM SA, the French central depository that became Euroclear France.
Théodore was chairman of CLEARNET SBF SA, a subsidiary of Euronext that ran Euronext clearing operations, until its merger with LCH at the end of 2003 to become LCH.Clearnet.
Théodore held a law degree from the University of Paris and was a graduate of the Institut d'Etudes Politiques de Paris and the Ecole Nationale d'Administration (ENA).
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