Siegburg is located approximately 8 kilometres east of the river Rhine, at the confluence where the Agger joins the Sieg, in the southeast corner of the Cologne Lowland. Neighbouring towns include Troisdorf, Lohmar, Sankt Augustin and Hennef. The nearby cities of Cologne and Bonn are easily accessible through good transport links. The highest point of the urban area is 220m above sea level (NHN) in the Braschoß area and the lowest point is just under 54m above sea level at the mouth of the Agger.