The 125 staff were told yesterday that the operation in in Chepstow, Monmouthshire will shut its doors by the end of September.
The renewables division – which specialises in fabricating wind turbine monopoles – had been up for sale since last December.
But the Enquirer revealed last month that the sale plans were dealt a massive blow when the Government suddenly decided to pull wind farm subsidies.
Steelwork firm Mabey said that 50 potential buyers had been in touch with one suitor in exclusive talks for the last three months.
But the deal fell apart last week.
Juliette Stacey, Chairman of Mabey Bridge, said: “This is not a decision that we have taken lightly and we understand that this is a very difficult time for our people. Since December 2014, we have made every effort to try to find a buyer.
“The uncertainty of market conditions for the UK onshore wind industry in the longer term has been a contributing factor.
“The priorities for us now are to support our affected employees in whatever way we can, and to ensure that the longer-term future of Mabey Bridge as a whole is secure.
“We will provide our people with as much information and support as possible over the coming weeks.
“Mabey Bridge will continue to be run from Lydney, Gloucestershire, providing high quality bridging and infrastructure solutions in the UK and overseas.
“We will now focus on building a stronger and more sustainable future for Mabey Bridge.”