Penrhos Leisure Village centres around a long stretch of coastline and a collection of refurbished former estate buildings on 200ha of land on the outskirts of Holyhead.
The project includes 1,100 lodges, cottages and homes, an enclosed subtropical waterpark and walking and cycle routes set within the fabric of the Penrhos coastal park.
Developer Land & Lakes announced the monster scheme five years ago with the project led by masterplanner and landscape architect Planit-IE and TEP acting as ecology consultant.
The development won planning permission from the Isle of Anglesey County Council but because the site was in an area of outstanding natural beauty it automatically went before the government.
But the project received a big boost two years ago when the Welsh government decided not to 'call in' the planning application.
Land and Lakes and the council were then locked in legal negotiations for around a year over a section 106 agreement, which has now been all-but rubber stamped.
The developer agreed a £20m deal to mitigate the impact of the development on Holyhead. Under the agreement Land and Lakes must provide and maintain 29ha of publicly-accessible areas including coastline, paths and a 700sqm sports centre with outdoor sports pitches.
Builders are now set to start creating the leisure park, with 500 lodges and cottages at Penrhos Coastal Park, a further 315 lodges at Cae Glas, and 320 homes in the Kingsland area.
Some of the new accommodation will house workers if a new Wylfa nuclear power plant is built on the island. Construction dates have not been finalised.
Council chief executive Gwynne Jones, said: "This was the largest planning application ever to be considered by the council.
"It was vital, therefore, that the many provisions included in the agreement were examined carefully and meticulously.
"The terms agreed with Land and Lakes will bring in excess of £20m to mitigate the possible impacts an application of this scale will have on the area."
Anglesey MP Albert Owen said: "The agreement was about making sure the local community gets a benefit, not just the developers.
"Land and Lakes has an opportunity to deliver high-quality tourist accommodation that will benefit the whole island and of course Holyhead."
Land and Lakes' director of operations Gill Ronayne said: "The section 106 agreement is a very complex document detailing all our planning obligations. It’s not unusual to take time to finalise.
"Land and Lakes is doing everything in its power to complete this agreement as soon as possible, and we are confident that we will now have sign off before the end of April."
An Anglesey Council spokesman said: "We’re working with all parties involved to complete the legal agreement with a view to releasing planning consent as soon as possible."