It flows from the hills surrounding Calne and meets the Avon about a mile upstream of Chippenham.

The Marden rises just north of the valley of Ranscombe Bottom near Calstone Wellington in Wiltshire.

The river is then joined by the combined Fisher's and Cowage brooks before turning to the north-west, past the village of Stanley.

1.5 miles (2.4 km) later it joins the Bristol Avon to the north-east of Chippenham.

[citation needed] A branch of the Wilts & Berks Canal, opened in 1810, paralleled the course of the Marden west of Calne.