It is the original Severn road crossing between England and Wales, and took three and a half years to build,[7] at a cost of £8 million.

[10] Following the completion of the Second Severn Crossing, the section of motorway from Olveston in England to Magor in Wales was designated the M48.

The first proposal for a bridge across the Severn, approximately in the same location as that eventually constructed, was in 1824 by Thomas Telford, who had been asked to advise on how to improve mail coach services between London and Wales.

[11] The growth of road traffic in the early 20th century led to further calls for improvements, and in the early 1920s Chepstow Urban District Council convened a meeting of neighbouring local authorities to consider a Severn crossing to ease congestion and delays on the A48 passing through the town.

In 1935 Gloucestershire and Monmouthshire County Councils jointly promoted a Parliamentary Bill to obtain powers to build the bridge over the estuary, with 75% of costs to be met by the Ministry of Transport from the Road Fund.

[12] After the Second World War, plans began to be made for a nationally funded network of trunk roads, including a Severn Bridge, for which the contract was awarded to Mott, Hay and Anderson, with Freeman Fox and Partners.

[15] In January 1977, it was announced that bridge traffic would be restricted to a single lane in each direction following the discovery of several weaknesses in the ten-year-old structure.

A system of rubber casing on the cables with dry air circulation, as used on the Forth Road Bridge, was installed in 2007–2009 in a move to halt the progress of the corrosion.

It consists of a single large cable stayed section with two single-leg pylons supporting the bridge deck from the centre of the roadway.

The deck is an orthotropic box girder similar to the Severn Bridge but has a different appearance as it has two sets of cable stays on each of two towers.

[33] For a small car the bridge toll represented a saving of 7s (£0.35) on the price of the ferry crossing, at that time 9s 6d (£0.475).

[35] In the 2016 United Kingdom budget George Osborne, the Chancellor of the Exchequer, announced that toll charges on the Severn crossings would be halved in 2018.

[36] The Welsh Liberal Democrats leader Kirsty Williams called the cut "pathetic" and said, "The Chancellor is cynically acting as if he is doing commuters a favour, but the fact is that he wants to keep this unfair tax on entering Wales."

[37] In July 2017, the Welsh Secretary, Alun Cairns, announced that tolls would be abolished by the end of 2018, claiming that this would boost the South Wales economy by around £100m a year.

[40] On 17 December 2018, all toll lanes were permanently closed, officially marking the start of a toll-free journey into Wales for the first time since the bridge's construction.

[51] Ownership of the bridge and the Second Severn Crossing returned to the UK government on 8 January 2018 when the revenue required to build and maintain them, as defined in a Concession Agreement with the Secretary of State for Transport, had been collected.