His father Joseph came from an old Dauphinois family which included the famous doctors Jean (1671–1727), army surgeon, and Jacques (1696–1764), physician in ordinary to the king at Grenoble.
It was ennobled in 1788 thanks to Léon's great-grandfather Philibert-Augustin de Beylié (1730–1797), who had a military career in France's colonies before being elected the representative of Pondichery and the East Indies in the 1789 Constituent Assembly.
Léon was decorated and mon 3 November 1870 made a knight of the Légion d'honneur before returning to Saint-Cyr to complete his training.
In spring 1882 he took two months' leave staying at several towns in Italy viewing culutral sites and art and buying various objects (often from the Middle and Far East), trinkets often without value.
This involved a total of five weeks in several Indian towns and cities, allowing him to publish his first brochure on a country and to collect punch daggers.