The line was authorised in 1900, and the Hon William Hall-Jones turned the first sod of the Stratford-Kawakawa Railway at Stratford on 28 March 1901 - Kawakawa, south of Ongarue, was to be the junction point with the North Island Main Trunk Line.
On 7 November 1932 the last spike was driven at Heao by the Prime Minister, the Right Hon. Gordon Coates, though the SOL was not handed over by the Public Works Department to the New Zealand Railways Department until 4 September 1933.