Young's Seafood has confirmed the closure of its Pinneys of Scotland plant in Annan.
It comes after consultation over proposals to move production from the Scottish site to Grimsby.
Cross-party efforts have been ongoing throughout that period to try to save hundreds of jobs.
The company said that it had not been able to find any "viable alternative" to closure which would now take place towards the end of the year.
"The decision to close the Pinneys site does not mean that collective consultation has ended," said a spokesperson.
"We intend to continue to meet with employee representatives on a fortnightly basis to discuss ongoing items, including redeployment opportunities."
The company said one-to-one consultations with staff would now take place.
"Our dedicated, skilled teams at Pinneys are a credit to our company and we will work hard to maintain the employment of our colleagues wherever possible," added the spokesperson.
"We have a long history of seafood production in Annan and, given that we have another factory in the town where we are a significant employer, we are committed to continuing to play a role in the local community."
Devastating news that Young’s are to proceed with Pinneys closure. Sadly redundancies now inevitable & imminent. Workforce have shown incredible professionalism throughout and deserve all available support. Priority now is to secure a new buyer to retain production at the site. pic.twitter.com/guNAagXo8a— Oliver Mundell MSP (@olivermundell) May 31, 2018
Scottish Secretary and Dumfriesshire, Clydesdale and Tweeddale MP David Mundell said it was "devastating news for Annan and the wider community".
"The fact we have been expecting it does not lessen the blow in any way," he said.
"The Pinneys workforce have really shown their mettle during this dreadfully difficult time.
"We owe it to them to fight on for the best possible outcome."
Enterprise Minister Paul Wheelhouse, said that despite the efforts to persuade Young's to keep some production on site it had been become clear the company wanted to focus on "extracting themselves" from the plant.
"The Scottish government and our partners in the action group will continue to work tirelessly to identify and support any potential new investor to the site," he said.
He said talks with interested parties would continue to try to keep as many jobs as possible on the site.
Dumfriesshire MSP Oliver Mundell said it was "devastating news" with redundancies now "inevitable and imminent".
He said the priority was to find a buyer to retain production on the site.
South of Scotland MSP Colin Smyth said few would be surprised by the confirmation of the closure and accused the company of "going through the motions" in the consultation.
However, he said the fact that it had been expected would not make the the news any less devastating for the families affected.
"With other recent bad jobs news at Edinburgh Woollen Mill and Arla Creamery, it's clear that a jobs crisis is engulfing the area and the Scottish and UK governments' response has so far been wholly inadequate," he said.