It lies in the German federal states of Lower Saxony and North Rhine-Westphalia.
As a natural region the Middle Weser Valley, which consists of flood plains and river terraces, is a strip of land up to 10 kilometres (6.2 mi) wide on both sides of the Middle Weser.
It is counted as part of the Dümmer Geest Depression and the Middle Weser Region.
The towns of Porta Westfalica, Minden and Petershagen all lie in that part of the Middle Weser Valley that within North Rhine-Westphalia, in the district of Minden-Lübbecke.
On the Lower Saxon side of the border, in the district of Nienburg/Weser, the Middle Weser Valley is home to the municipalities of Stolzenau, Landesbergen, Steyerberg, Weser-Aue, Nienburg/Weser, Heemsen, Eystrup and Hoya.