Haberdashers Adams has admitted girls to its sixth form for 30 years but the rest of the school has been resolutely all boy since 1656, when Oliver Cromwell ruled the land as Lord Protector.
James Penney, who chairs the Newport school's governing body said the decision to go fully co-educational from September 2024 meant exciting times are ahead.
“We very much believe this is an auspicious time for Haberdashers’ Adams; our ethos ‘Traditional values, modern approach’ has never been more relevant and appropriate, and we are looking forward to some very exciting times ahead,” he said.
The school carried out a consultation and announced the results to staff, pupils, parents and alumni on Monday.
The new admissions policy will be in place for the entrance test in September 2023 with the first cohort of Year 7 girls arriving in September 2024.
A school statement said the decision means there will be "no reduction in opportunities for boys in the local area, as priority will still go to local pupils first".
It added: "Having more local children allows them to take part in after-school clubs, events and fixtures which is currently a significant challenge for many of our pupils who live further away.
"We will, of course, continue to have many day places available for children from further afield and, as a state boarding school, Haberdashers’ Adams can offer boys from further afield the option to board."
The school will hold a public information evening next month, with details to be advertised soon, as well as including information in the upcoming Year 7 Open Day on January 31.
At Easter the school will appoint its head of sixth form, Charlotte Harman, as the deputy head in charge of girls.
"It will be her role to focus not just on the logistical side of all the necessary preparations, but also on the social and emotional aspects of provision for this change to the school," said the statement.
"As such, we are very confident that with a year and a half before girls actually arrive on site we are well-placed to be able to prepare for this exciting change."
Headmaster Gary Hickey said: “Girls have thrived in our sixth form for 30 years. This next exciting step is part of the natural evolution of Haberdashers’ Adams. It’s a wonderful opportunity to offer a first class grammar school education to boys and girls in the heart of Shropshire.”
Haberdashers’ Adams was founded by William Adams, a merchant haberdasher with family connections in the area.
He established his school in Newport in 1656 during the Interregnum, with permission from Oliver Cromwell, and appointed the master and wardens of the Haberdashers’ Company as governors. He left money and estates to the company to support the school.