The owners of the Anglesey Aluminium site at Holyhead have entered into an option agreement with developer Land & Lakes for the development, subject to planning permission.
The Welsh Assembly Government and the Isle of Anglesey County Council have been working with Anglesey Aluminium and Land & Lakes to help bring forward the proposal.
The council expects to receive a planning application in around 12 months time.
Anglesey commissioner responsible for economic development Alex Aldridge said the scheme would give a major lift to Holyhead and the wider Anglesey economy as well as adding to the island’s tourism offer.
Newly appointed council leader Bryan Owen added: "The importance of 600 much-needed jobs on Anglesey, which has borne the brunt of the recent economic downturn, is huge.
"I'm also pleased that Land and Lakes recognises the environmental importance of the area and that it has made a clear commitment to using the local supply chain and services."
First Minister Carwyn Jones said: "Anglesey also has the potential to play a huge role when it comes to our renewable energy needs. We remain a committed partner of the Energy Island Programme and we are keen to pursue any opportunities presented through the site coming into new ownership to further low carbon energy projects."