[1] 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.

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.

He firmly believed that financial integration of Europe was an essential and natural step in the development of the European economy.

He was also simultaneously a partner in the U.S. investment bank Kuhn, Loeb from 1953 until 1964 through a holding company[2] to avoid the restrictions of the Glass–Steagall Act.

He died in London in 1982, survived by his wife Eva Maria (née Philipson), a son, a daughter and four grandchildren.