Wilko in Altrincham is set to close in the next few weeks after a rescue deal for the chain fell through.
There had been hopes that a bid by HMV's billionaire owner, Doug Putman, could keep the George Street store alive - as well as up to 300 others - but his bid collapsed this morning.
The GMB union has now confirmed that all of Wilko's 400 stores across the UK will close by early October.
The news will be a huge blow for all 12,500 staff employed by the family-owned business.
Putman said: It is with great disappointment that we can no longer continue in the purchase process for Wilko having worked with adminstrators and suppliers over several weeks to seek a viable way to rescue it as a going concern.
"A stable foundation could not be secured to ensure long-term success for the business and its people in the way that we would have wanted."
Founded in 1930, the cash-strapped chain announced in August it had collapsed into administration.
Nadine Houghton, national officer at the GMB union, said: "Wilko was far more than a brand, a retailer or the products it sold, it was the thousands of loyal team members now facing an uncertain future.
"Wilko may have ceased genuinely being a family brand many years ago, but the staff kept the real family ethos of Wilko alive until the very end. It is the family that Wilko colleagues made for themselves that will be missed the most."
