The town stands on the River Darwen, which flows from south to north and is visible only in the outskirts of the town, as within the town centre it runs underground.
The area around Darwen has been inhabited since the early Bronze Age, and the remains of a barrow from approximately 2000 BC have been partially restored at the Ashleigh Barrow in Whitehall. Artefacts including a bronze dagger and urns containing human ashes were found, and a small number of these finds are now on display at Darwen Library Theatre. The Romans once had a force in Lancashire, and a Roman road is visible on the Ordnance Survey map of the area. Mediaeval Darwen was tiny; little or nothing survives. One of the earliest remaining buildings is a farmhouse at Bury Fold, dated 1675. Whitehall Cottage is thought to be the oldest house in the town, and was mostly built in the 17th and 18th centuries but contains a chimney piece dated 1557.
Like many towns in Lancashire, Darwen was a centre for textile manufacture during the Industrial Revolution. Samuel Crompton, inventor of the spinning mule, lived there for part of his life. Rail links and the Leeds and Liverpool Canal arrived in the mid-19th century. The most important textile building in Darwen is India Mill, built by Eccles Shorrock & Company. The company was ruined, however, by the effects of the Lancashire Cotton Famine of the 1860s. Cotton manufacture was an important industry, and by 1907, the Darwen Weavers', Winders' and Warpers' Association had more than 8,000 members in the town.
Much of the town was built between about 1850 and 1900; placenames, date stones in terraces, and the vernacular architecture of cellars, local stone, locally-made brick, pipework and tiles and leaded glass, the last now mostly gone, reflect this. It was one of the first places in the world to have steam trams. The arrangement of town hall, market, public transport, eating/hotel facilities and the pre-suburban mixed-size vernacular housing, with local variations according to topography, is very characteristic of Northern England. The year 1900 perhaps represents the peak of Victorian optimism in the area. The working classes were then much more identifiable as masses than now. The rise of the Labour Party from about 1900 coincided with a decline in the Liberal Party, which followed the Manchester School in economics, increasingly seen as permitting unjustified exploitation. However, Darwen usually voted for the Conservative Party until a Conservative government made unpopular administrative rearrangements in the early 1970s.