Lieutenant Erik de Laval served in the Kungl. Svea Artillereregemente (Royal Svea Artillery Regiment) in Stockholm. At the Swedish modern pentathlon trials he placed first (April 1912) and third (May 1912), after he had missed the first competition in November 1911 due to an injury. At the Stockholm Olympics de Laval competed together with his brothers Georg and Patrik, both also military officers. George de Laval eventually won the bronze medal after leading before the last event, while Erik was disqualified in the cross-country riding. After World War I, only Erik, the youngest brother, competed again in Antwerpen, taking the silver medal after winning two of the five events, shooting and riding.
At the beginning of World War II, de Laval was military attaché at the Swedish Embassy in Poland and visited concentration camps several times. In 1942 he was seconded to the Swedish legation in Washington, DC with the rank of colonel. In this capacity he visited camps of Japanese internees, notably in Hawai’i. Based on his experiences in Poland de Laval wrote books about the country’s modern history and a biography of the Polish leader Marshal Piłsudski. In 1948, he was stationed in Damascus as a member of the UN mission mediating the Arab-Israeli conflict of 1947-48.
Sweden