He was born in the village of Seeburg,
Germany (today part of
Bad Urach), the only child of Georges Siegmund Warburg and his wife, Lucie, who raised young Siegmund on an estate (Uhenfels Castle) in
Swabia in
South West Germany far away from the main branch of the family, which operated the second largest bank in
Hamburg. Siegmund had a sincere and deep affection for his mother who taught him to have a critical and inquisitive mind. In the period immediately before the
Second World War he worked under cover for the Z Organisation, a highly secret offshoot of
MI6/SIS, and reported from
Switzerland on his regular meetings with
Hjalmar Schacht, then the president of the
Nazi German Reichsbank and thus the most powerful German banker. He was forced to flee the
National Socialist regime of
Adolf Hitler and moved to the
United Kingdom in 1934 where he co-founded
S. G. Warburg & Co. in 1946 with
Henry Grunfeld. In the UK, Siegmund was considered an 'upstart' to the establishment in the
City of London. His most famous achievement was the establishment of the EuroBond market. He firmly believed that financial
integration of Europe was an essential and natural step in the development of the European economy. He was a firm supporter of European integration and involved in organizations dedicated to this goal, like the
Action Committee for the United States of Europe, the United Kingdom Council of the
European Movement, the
European Foundation or the
Bilderberg group (Warburg 2010: pp. xx, 460). The firm that he created with Grunfeld, S.G. Warburg & Co., was a major
British investment bank (merchant bank at the time), and Siegmund was the bank's managing director until the 1970s—when although he officially had retired and was living in Switzerland, still retained a personal secretary to draft correspondence and assist with the operations of the firm. Control of the firm S.G. Warburg and Co. was retained through a family controlled holding company called 'Mercury Securities', where stock was allocated to S.G. Warburg & Co. partners as well as his
Swedish wife and children. The firm S.G. Warburg & Co. was acquired by
Swiss Bank Corporation creating SBC Warburg in 1995. After the merger of SBC with UBS AG, the investment bank was rebranded UBS. He was also simultaneously a partner in the U.S. investment bank
Kuhn, Loeb from 1953 until 1964 through a holding company to avoid the restrictions of the
Glass–Steagall Act. ==Personal life==