ARDS Borough Council have accepted an offer of almost £1m from the executive to keep open and redevelop the Exploris Aquarium.
The green light will also be needed from the new North Down and Ards District Council before it can proceed.
Exploris in Portaferry houses marine exhibitions and a seal sanctuary on the shores of Strangford Lough.
Councillors also agreed a specialist contractor should be appointed to help rejuvenate the aquarium.
The offer is made up of £914,000 in capital funding and £120,000 in revenue funding.
Last month, the Executive approved funding to save the aquarium.
Finance Minister Simon Hamilton said £900,000 capital funding would be earmarked for the aquarium, which had been under threat of closure by its owner, Ards Borough Council.
The council said that the £600,000 annual cost of running it was too high.