Nelson is a town and civil parish in the Borough of Pendle in Lancashire, England, it had a population of 33,617 in 2021. Nelson is 3 miles (5 km) north of Burnley and 2 miles (3 km) south-west of Colne. Nelson developed as a mill town during the Industrial Revolution.

An Iron Age hillfort called Castercliff is on a hill to the east of the town. The modern town spans the two parts of the township of Marsden in the ancient parish of Whalley. Little Marsden was on the south-west of Walverden Water, its lands considered part of the manor of Ightenhill and Great Marsden to the north-east, part of the manor of Colne. Great Marsden included the southern parts of Colne, and Little Marsden included all of modern-day Brierfield.

Walverden Water joins Pendle Water next to Nelson & Colne College, with that river forming the boundary of the Forest of Pendle. Both the manors and forest were parts of the Honour of Clitheroe. The lord of Clitheroe had a mill on the river in 1311, thought to have been sited near the confluence with Clough Head Beck, where Scholefield Mill now stands. There is also evidence of an ancient fulling mill further upstream. A small chapel is thought to have been built during the reign of Henry VIII on the site of St Paul's Church.

The forest of Pendle was made famous by the Pendle witch trials of 1612. One of the accused in the less well-known witch trials of 1634, Margaret Johnson, confessed that she first met her familiar in Marsden.

A small mill had been established by the Ecroyd family at Edge End as early as 1740, and they started Lomeshaye Mill as a water-powered spinning mill in 1780. The coming of the Leeds and Liverpool Canal in 1796, followed by the East Lancashire Railway Line in 1849, spurred its development as an industrial town, with an economy based mainly upon cotton weaving. The first Ordnance Survey map of the area, published in 1848, shows three small villages: Marsden (around St Paul's), and Hebson and Bradley, both on Walverden Water in the modern-day centre of town. Also apparent are the estates of Marsden Hall to the east and Carr Hall across Pendle Water to the north-west, as well as the turnpike roads of the Marsden, Gisburn and Long Preston trust (Scotland Road) heading north, and the Blackburn, Addingham and Cocking End trust (Manchester Road) heading east.

Brierfield railway station was originally called Marsden, and Nelson railway station was known as the Nelson Inn station, Great Marsden, after the adjacent public house, the Lord Nelson Inn (named after Admiral Lord Nelson). As the villages developed into a town, the name Nelson was chosen to differentiate it from Marsden across the Pennines in the neighbouring (West Riding of Yorkshire).

There was a worsted mill at Lomeshaye close to a "cotton factory" and another cotton mill along the canal at Reedyford by 1848. Walverden Mill in Leeds Road was built in 1850, and it was soon followed by others. From 1862, Phoenix Foundry, the steam engine factory of William Roberts, stood at the site of the shopping centre's car park, and has been called "Nelson's most significant engineering site". By 1891, there were 57 cotton spinners and manufacturers listed in Nelson. The largest had 1,950 looms and the smallest only 8.

The cotton industry was the most important in the town, and by 1910, more than 12,000 local workers were members of the Nelson and District Power-Loom Weavers' Association.