Council chiefs say plans to build a new moden home for Holyhead High School have received "overwhelmingly positive" support.
Around 900 pupils are set to move into a purpose-built £66 million building near the town's leisure centre by September 2030.
Anglesey Council agreed to publish a statutory notice on Tuesday, following a public consultation on its proposals held during the summer.
Over a thousand people took part - with 79% of stakeholders and learners in favour of building a new school.
Cllr Dafydd Roberts, who holds the education portfolio, said: "The positive response to our statutory consultation has provided the confidence needed to forge ahead with these proposals for a new Ysgol Uwchradd Caergybi."
“Today’s decision to authorise the publication of a statutory notice is an exciting step towards opening a new school building. The proposal also represents our commitment to the future of education and Welsh language in the town and wider Holy Island.”
“The input provided from everyone connected to Ysgol Uwchradd Caergybi will help us shape this project going forward.”
The council says the current school on South Stack Road is approaching the end of its working life and facing significant maintenance costs - with the discovery of RAAC concrete in September 2023 affecting pupils' education.
The new building is aimed at providing more modern facilities and more green, open spaces, as well as ensuring there are enough secondary school places to meet the needs of 11-18 year olds both now and in the future.
But the plans have not been without criticism - some of those who responded to the consultation argued the new site was too far away from the town centre, while others wanted the current school to be redeveloped.
The council says the proposed site is the only one that meets Welsh Government guidelines, which require 31,625m² for a new building, not including playing fields.
The current site is only 27,000m2 and would therefore be unsuitable for redevelopment.
The whole project is also dependent on ensuring financial support from the Welsh Government - and it's hoped the estimated costs will be met jointly with the council through mutual investment.
Aaron C Evans, Anglesey Council's director of education, said: "Council officers have considered various options for the future of secondary education provision in the Holyhead area."
"We’re pleased that the Executive...agreed that a new school building for Ysgol Uwchradd Caergybi is the best way forward."
"Creating a new modern school building would be a significant investment in education in Caergybi and wider catchment area and would also ensure the long-term sustainability of secondary education in the area."
"A new school building with specialist modern learning facilities of the highest standard will also help ensure the best possible educational experiences and outcomes for young people; and support the aims of the county council’s 'Modernising Learning Communities and Welsh Language' strategy."
The council will formally publish its statutory notice early next month.


Menai Bridge to fully reopen on Friday
Restrictions for Caernarfon fireworks display
New Llanfethlu estate welcomes tenants
Bangor: views sought on extra police powers
Ten-year plan for Welsh language education