The retailer's plans to have an anchor site at a former Roches Stores outlet in the Wilton centre in Cork, and to retain all staff, appeared to have collapsed in a row over lease charges.
This put in jeopardy the jobs of 172 store staff.
M&S, which is expanding in the Republic, claimed the centre's owners, a business consortium, sought €1.8m for the lease - more than twice what it had agreed.
The owners initially claimed M&S had pulled out because it was being offered 20,000 sq ft, not the whole site. Talks had got under way with other "top retailers", it added.
Staff, backed by union Mandate, staged protests in Cork. Later the centre's owners said they had instructed their agents to reopen talks with M&S.
A spokesman for M&S insisted the original deal was for the entire 45,000 sq ft site and the jobs of the 172 staff depended on this being honoured. He added: "We intend to spend €8m-€10m on the fit-out - a very significant investment."
Trade minister Micheál Martin, in whose constituency the store is located, has intervened in an attempt to save the deal.