Born in France, at Besançon, in the family of a watchmaker and inventor. He finally settled down in Romania in 1873, where he was for several years the administrator of the Royal Domains, from Broşteni and Sinaia. The beginnings of entomological and malacological research in the south and east of Romania are related to his name.
Besides fauna and flora, Montandon became acquainted with people and places that were described in his works, that remained to us today as a valuable documentation of that time. Montandon especially studied heteroptera, becoming one of the greatest hemipterologists in the world; he described more than 500 new species and subspecies , publishing more than 100 works, in the most important specialized reviews.
He was a member of a great number of scientific societies, and since 1905, a corresponding member of the Romanian Academy (foreign section). He was awarded by King Carol I with the Crown of Romania with knight grade and with the Star of Romania.
Between 1896 – 1907 he worked as the assistant of Dr. Grigore Antipa, fully contributing to the organization of the new Museum of Zoology, that is today “Grigore Antipa” National Museum of Natural History from Bucharest.
The great self-educated naturalist died in Cernavodă, and left behind not only his written work but also vast collections of insects and molluscs, that are found today both in “Grigore Antipa” Museum and also at the Museum of Natural History from London.