The sections from Unna-Königsborn to the former Dortmund South station and from Dortmund-Dorstfeld to Dortmund-Mengede is now an entirely two-track electrified railway and is served by the Rhine-Ruhr S-Bahn (lines S 2 and S 4).

The line was built by the Royal Westphalian Railway Company (German: Königlich-Westfälische Eisenbahn, KWE) to connect its network, which at that time mostly ran through northern and eastern Westphalia, to the Ruhr area in the west in order to serve the lucrative traffic from its coal mines and factories.

As early as 1847 the Cologne-Minden Railway Company (Cöln-Mindener Eisenbahn-Gesellschaft, CME) had opened the Dortmund-Hamm leg of its trunk line.

The Westphalian station in Dortmund was next to the Rhenish station, built two years earlier by the Rhenish Railway Company (Rheinische Eisenbahn-Gesellschaft, RhE) at the end of its line along the Wupper from Düsseldorf and its line along the Ruhr from Osterath.

On 19 November 1874, the RhE opened the last part of its Ruhr line from Dorstfeld for passengers.

The Hamm-Osterfeld line was built on the section between Horst and Osterfeld from 1 October 1901 and later put into operation.

The Gelsenkirchen-Bismarck–Hugo junction–Gelsenkirchen-Horst section is now a single-track non-electrified freight line and connects to the network of RBH Logistics GmbH (now part of DB Schenker Rail).