[3] A report by the Railway Advisory Board from October 1911 recommended a route to Mount Barker branching off between Bridgetown and Manjimup rather than at Bridgetown as the most advantageous west-east route for a railway.

[4] The Manjimup Mount Barker Railway Act 1926, an act by the Parliament of Western Australia assented to on 24 December 1926,[5][6] authorised the construction of a 161-kilometre (100 mi) long railway line from Manjimup to Mount Barker.

Further north, the Boyup Brook-Cranbrook Railway had been authorised days before the Manjimup Mount Barker one.

[8] The survey for the Manjimup to Mount Barker railway line commenced in October 1927 from the western end.

At this point in time, the state government did not close lines, despite only one third of the ones in Western Australia running at a profit, and felt obliged to keep lose-making lines open which had attracted settlers through its construction.