John Milne, a civil engineer, published his Observations on the tidal currents at Leith; with plans for the improvement of the port (31 pp, with map) in Edinburgh in 1835. A second edition appeared the same year. He gained considerable experience working on various harbour projects in Scotland, England and Ireland. In December 1849 he arrived in Durban, where he worked under the harbour master as Natal's first harbour engineer. After a detailed study of the sand bar across the harbour entrance he proposed that the harbour mouth be narrowed by building a 600 m long pier from the Point, and a parallel but shorter breakwater from the Bluff. This recommendation rested on the assumption that tidal scouring would deepen the mouth from an initial two metres to about eight metres. The necessary work was started late in 1852, but the new Lieutenant-Governor of the Colony, John Scott, stopped the project in April 1857 and ordered an inquiry. As a result Milne resigned (or was dismissed from) his post. Scott's own attempts to improve the harbour were costly and futile.
Milne also built a drain to clear the Eastern Vlei of surplus water. Known as Milne's drain, it carried flood water into the bay when the Umgeni River bursts its banks and flooded the vlei. For many years imported timber, off-loaded from ships at high tide, was floated up Milne's drain to the timber yards near the east end of Smith Street.
When the railway line from Durban into the interior was started in 1876, two routes were considered. One of these had been proposed and provisionally surveyed by John Milne in 1868. From Durban it ran some 26 km along the valley of the Umhlatuzana River and then switched over to the valleys of the Umlazi and Umadodo Rivers before reaching its highest point a few kilometers north-west of Camperdown and proceeding over more elevated terrain to Pietermaritzburg. Though some 32 km shorter than the alternative route, it was rejected because of the possibility that the line would be flooded in the river valleys, and because it ran far from existing roads.
Around 1875 a committee of inquiry chaired by advocate Harry Escombe (later Chairman of the Natal Harbour Board) consulted Milne, then in his seventies, on the improvement of the harbour, but owing to financial constraints no action was taken. The tugboat John Milne was named after him in 1895.