It was designed by the New South Wales Government Railways, and built by W. Rowe and W. Smith (tunnel)[2] and Mr. McDonald (vent shaft).

With the use of longer or double headed trains, smoke problems necessitated installation in 1908 of a forced air fan at the northern end of the tunnel.

It is part of a notoriously steep section of the Illawarra line south of Waterfall used in the late 19th century by steam trains and bypassed by the Helensburgh deviation in 1919.

The Otford tunnel is of technical significance as an important engineering work in the early construction of the Illawarra line and was also used during the second world war as part of an explosives program.

[4] Otford railway tunnel was listed on the New South Wales State Heritage Register on 2 April 1999 having satisfied the following criteria.

The Otford tunnel is of historical significance as a major engineering work built 1888 to connect the Illawarra line to Sydney.

It is part of a notoriously steep section of the Illawarra line south of Waterfall used in the late 19th century by steam trains, and bypassed by the Helensburgh deviation in 1919.

[4] The place is important in demonstrating aesthetic characteristics and/or a high degree of creative or technical achievement in New South Wales.

The Otford tunnel is of technical significance as an important engineering work in the early construction of the Illawarra line.

[4] The place has potential to yield information that will contribute to an understanding of the cultural or natural history of New South Wales.