Ambly-Fleury is located some 10 km east by south-east of Rethel and some 23 km north-west of Vouziers. Access to the commune is by road D983 from Seuil in the west passing through the heart of the commune just south of the village and continuing east to Givry. The D45 minor road also comes from near Amagne in the north-west through the village then south to Mont-Laurent. Apart from the village there are also the hamlets of Ambly-Haut and Fleury on the D983 to the east of the village. The commune consists entirely of farmland.
The Canal des Ardennes passes through the heart of the commune parallel to the D983 in the west then continuing north-east out of the commune. The Aisne river also passes through the commune from the west passing to the north of the village then meandering though the commune and forming part of the northern border. The Ruisseau de Saulces Champenoises flows from the south through the commune to join the Aisne.
In 2009 the commune had 134 inhabitants. The evolution of the number of inhabitants is known through the population censuses conducted in the commune since 1793. From the 21st century, a census of communes with fewer than 10,000 inhabitants is held every five years, unlike larger towns that have a sample survey every year.[Note 1]
^At the beginning of the 21st century, the methods of identification have been modified by law No. 2002-276 of 27 February 2002 , the so-called "law of local democracy" and in particular Title V "census operations" which allow, after a transitional period running from 2004 to 2008, the annual publication of the legal population of the different French administrative districts. For communes with a population greater than 10,000 inhabitants, a sample survey is conducted annually, the entire territory of these communes is taken into account at the end of the period of five years. The first "legal population" after 1999 under this new law came into force on 1 January 2009 and was based on the census of 2006.