Untergriesbach is in the southern Bavarian Forest and extends high above the deep valley of the Danube. The height of the market town is 565 meters above sea level. Via the Bundesstraße 388 it is connected to Passau (22 km) and in the opposite direction to the Upper AustrianHaslach (32 km).
On 1 October 1971, the previously independent municipality Lambsdorf was incorporated. On 1 January 1972 Gottsdorf and Schaibing were added. Oberötzdorf followed on 1 March 1972.