Robert passed the diplomatic service examination in 1936, and joined the private office of Paul-Henri Spaak in April 1937.

As an officer in the Belgian Army reserve on the outbreak of World War II, Robert Rothschild returned to his regiment and his brother Marcel started his service at the Brigade Piron.

He made his way to London to join the Belgian government in exile of Hubert Pierlot, which posted him to the diplomatic legation in Lisbon (Portugal).

Under pressure from the French, who hoped to protect their interests in Indochina, Belgium declined to recognise the People's Republic of China for the next 20 years.

[4] In 1954, Rothschild was appointed chef de cabinet of Paul-Henri Spaak at the Belgian foreign ministry.

"[5] Robert was due to join the Belgian delegation at NATO after the summit conference in Paris in 1960, between Nikita Khrushchev and Dwight D. Eisenhower.

But, because of the Lockheed U-2 spy plane crisis, the conference was a failure and, so, Rothschild was sent to the Belgian Congo as number two to the governor.

He arrived in Leopoldville (now Kinshasa) two days after the rebellion by the constabulary, egged on by the Pan-Africanist Congolese independence leader, Patrice Lumumba.