Feldkirchen is located on the northern edge of the Klagenfurt Basin at the junction of the federal highways (Bundesstraßen) B 93 Gurktal Straße toward Friesach, B 94 Ossiacher Straße to Villach and B 95 Turracher Straße to Klagenfurt. Both the Glan river and the small Tiebel, main inflow of Lake Ossiach, run though the town.
The settlement may have developed at the site of the former Beliandrummansio along the Roman road from Teurnia near Spittal an der Drau to Virunum, capital of the Noricum province. A Roman tombstone of the 2nd century is included into the walls of the Saint Michael filial church. The earliest mention of Feldkirchen is as Ueldchiricha ("Church in the Fields") in an 888 document by Arnulf of Carinthia. The parish church Maria im Dorn, a Romanesque basilica with a Carolingian choir, is one of the oldest sacred buildings in Carinthia.
Feldkirchen, once an estate of the Eppenstein noble family, was bequeathed to the Diocese of Bamberg in 1166. The bishops had the Amthof erected, the former seat of the local administration, today a place for cultural events and a small museum. Finally Maria Theresa of Austria acquired Feldkirchen in 1759. The village of Markstein south of the town centre is a former checkpoint at the border between the Austrian Empire and the Upper Carinthian part of the short-lived Napoleonic Illyrian Provinces. The building of a customs station and a border stone remained. Feldkirchen received town privileges in 1930.
According to the 2001 census, Feldkirchen has 14,030 inhabitants. Of that, 77.1% admit themselves to the Roman Catholic Church, 12.0% are Evangelist, 0.8% belong to the Orthodox Church, and 5.1% are Muslims. 2.0% are non-religious.