The line operated from 24 October 1879 until 16 August 1967 and existed for the sole purpose of conveying coal from mines to the port of Westport.
In September 1875 the Wellington Coal Mining Company called for tenders for a private line from a junction with the Seddonville branch at Waimangaroa to a site 1.6 kilometres (1 mile) up the Waimangaroa River adjacent to the company's mine.
In 1877, good quality coal was found high on the Mount Rochfort Plateau and the Westport Colliery Company was formed to exploit it.
Tenders to extend the Wellington Coal Mining Company's railway by 1.1 kilometres (0.7 miles), and build the Denniston Incline, closed on 30 April 1878.
[8] The Conns Creek Branch was operated throughout its life by the New Zealand Railways Department (NZR), which also supplied all locomotives and rolling stock.
Traffic was in significant decline by the time the railway passed into NZR ownership, and trains no longer ran through to Westport; a shunting locomotive based in Waimangaroa shuttled wagons up and down the branch, and Seddonville Branch trains took the wagons between Waimangaroa and Westport.
[14] Although remnants of closed railways deteriorate and disappear over time due to natural and human activity, some remains of the Conns Creek Branch still exist.