Land and Lakes has purchased the land at Holy Island from Anglesey Aluminium Metals Ltd.
Once complete, the development will include 800 lodges and cottages, a spa and 320 houses on the site, which also covers nearby Cae Glas and Kingland.
Buildings on the Penrhos estate will also be restored and work is expected to begin in 2018.
Land and Lakes said the resort would generate hundreds of jobs and training opportunities and would maintain public access to much of the Penrhos estate.
Some of the new accommodation would also house workers if a new Wylfa nuclear power plant is built on the island.
Economy and Infrastructure Secretary Ken Skates said the development would boost tourism and attract investment, jobs and affordable housing, while Anglesey MP Albert Owen said it would make the area a "top place" to experience modern facilities in a natural environment.
The original application for the Land and Lakes development was first put forward in 2011, following the closure of the town's Anglesey Aluminium plant.
The proposals were initially agreed in 2013, but it has taken since then to agree a section 106 agreement, which will see the firm contribute towards extra school places, doctors and council support services.
A firm behind plans to build a £120m holiday village on Anglesey has bought 600 acres of land for the development.