The historic Trinity House Academy in Hull, will admit girls from September 2022 under plans approved by the trust that runs the school.
The move, which follows a public consultation, will see the former marine training academy double its capacity from 120 to 240 students and move to a new location in the city.
Delta Academies Trust Chief Executive Officer, Paul Tarn, welcomed the decision and said: “The Trust will continue working in partnership with Hull City Council to develop the plans. The Academy will be central to a resurgent city, with new jobs and opportunities accessible to the young people of Hull.
"The aim is for the move to happen in time for September 2022. Our focus throughout has been on what is in the best interests of current and future students at Trinity House Academy.
“We have worked with The Brethren and local governors to ensure traditions at the school will be maintained, whilst creating an outstanding learning and teaching experience and offering greater opportunities to young people across the city.”
The school was founded in 1787 as a marine school for boys destined for careers at sea, and taught navigation and other maritime skills.
It was run by the seafarers' charity and guild Trinity House, and has remained boys-only and linked to the organisation ever since.
Initially private, it later entered the state sector as a technical school and has been a comprehensive academy since 2014.
A year later, it moved from its Victorian site to the old Hull Nautical College buildings after they had been vacated by the University of Lincoln.
Pupils still wear naval-inspired uniforms, maritime studies remains on the curriculum and activities such as sailing are available.
Hull Trinity House Academy Principal Graham Moffatt said: “We are looking forward to discussing next steps with students, staff and parents, and sharing the great opportunities this project will unlock for our school community.”
Under the plans, laid out earlier this year, girls would enter as part of a phased expansion, one year at a time, starting at Year 7 in September 2022.
In a consultation sent out to parents in March, the trust said it planned to move to a co-education school because it "supports equality of opportunity for all".
It also added it would allow local families to choose its "unique educational offer for their daughters as well as for their sons".
It also highlighted the fact that the number of women going into and succeeding in STEM (science, technology, engineering and maths) subjects is "increasing rapidly".
And the numbers of women who choose to go to sea as a profession has "increased dramatically" was noted as a reason.
Councillor Shane McMurray, of Hull City Council, said: “During several meetings with Delta Academy Trust my cynicism diminished very quickly. It is very clearly in the interest of young people within the city to have this school increase its capacity.
"Not only will they be inducting more young people into a school with a strong ethos and strong learning culture, but they will also be able to increase the breadth of their current curriculum to include more specialist subjects.
“All my initial reservations were overcome upon speaking with the academy who clearly had put in place a plan to mitigate potential issues. I have also had assurance that the school will work to have a positive impact in the local community that it will be amongst; beyond its immediate pupil numbers.
"It’s absolutely imperative that the young people of Hull have the best possible chance of accessing the new jobs and industries that have been and will be developing on our coast and this school is able to deliver this in an authentic way.
"I wish the very best future for the school, the staff and most of all the pupils of this school.”
Capt Dennis Robinson, Master Warden of The Brethren and on the Academy Advisory Body, supports the move.
He said: “Trinity House was the first Navigation School, established in 1787, by The Brethren, which was forward thinking indeed. Now, almost 250 years later, The Brethren realise that times have changed.
“Whilst the demand for British Seafarers has reduced overall, the numbers of women who choose to go to sea as a profession has increased dramatically and we know of all female crews on ships and aircraft.
“The Brethren would therefore support the school becoming co-educational, and extend the nautical ethos, education and training opportunities of the Academy to both sexes.
“For over 200 years, the school has been within the Trinity House Estate and the move to the old Nautical College buildings in George Street was a move away from The House.
“However, the links between The House and the school have remained strong, as has the ethos and character of the school.
“The Brethren are assured, and confident, that that ethos and character of the school, formed over many years, will remain as strong, if not stronger, if this initiative comes about.
“They are confident that the larger school will be every bit as academically successful as it has been in recent years with strong outcomes for the pupils, whether they take up a seagoing career or not."