The experienced civil engineer Samuel Morton Peto acted as contractor for the works with the majority of the tunnel being constructed using traditional cut-and-cover techniques.

Carrying a pair of tracks throughout its length, it has been periodically operated as a single-track only tunnel while remedial or improvement work was performed.

In addition, the tunnel has facilitated large amounts of freight movement to and from the Southampton Container Terminal and the rest of the UK.

During 2009–10, it was subject to extensive re-engineering works, successfully raising both its loading gauge and maximum speed for container traffic.

[2] It was decided to construct the majority of the tunnel using the traditional cut-and-cover method, with only a limited section (the portion running directly underneath the London Road) being actually bored out.

[3] The canal tunnel had itself proven difficult to construct, with various sections sinking or collapsing due to geological conditions, poor materials and improper supervision of the works.

Just over two weeks later, on Thursday 20 and Friday 21 May 1847, Captain Coddington, the Government Surveyor of Railway, was able to inspect the line for the Board of Trade.

The crossing of the new tunnel in no way affected this drainage...so the soil (a black Clay) continued firm enough to support the brickwork laid upon it.

But by the filling up solid of a portion of it, leaving a hollow interval...the accumulation of water in seeking an egress has entered into, saturated, and sodden the clay on which the new Tunnel stands, and it is now incapable of supporting its weight.

The remaining western section of the Canal Tunnel was drained and filled with flyash in the 1970s using shafts dug from the surface in order to stabilise the ground above.

[4] Between 1983 and 1985, British Rail decided to perform extensive engineering works to facilitate the movement of larger containers through Southampton Tunnel.

Additional journeys are made on the West Coastway Line from Southampton to London Victoria via Gatwick Airport, and on the Cross Country services from Bournemouth to various points in the north of England.