At a Parish Assembly on Wednesday evening, residents voted 48 to 43 in favour of a proposition to sell the former residential home, which overlooks the People's Park, for £2.9 million.
It emerged at the meeting that the investors looking to buy the site were the Columbia Group, a property firm that manages residential and commercial sites across the Island.
However parishioners also agreed that any sale should be subject to a ‘betterment clause’, meaning there would be restrictions on how much profit the new owner could make from the site.
That amendment was brought forward on the night by parishioner and former politician Edward Trevor.
After the meeting, Constable Simon Crowcroft told the JEP: ‘We now need to negotiate the betterment clause with the buyer which means they are going to be restricted on how much profit they can make and that has to be agreed by both sides.
'That is quite a big deal and they may walk away. I would say it really is a game-changer.'