They drew up initial plans in May 2003 to turn two former woolstores at the harbour into 15 self-contained residential apartments.
They own the two buildings, and lease the land they sit on from the Waitaki District Council.
Their plan went through the Resource Management Act process, getting approval from the Waitaki District Council in 2006 but was appealed to the Environment Court.
In April this year, the court released an interim decision in favour of the development, Judge Fred McElrea, commissioners David Kernohan and Dr Diane Menzies saying it would improve the appearance of and bring new life to Oamaru Harbour.
Visually, it would bring a "considerable improvement" to the present buildings.
The interim decision was subject to agreement on conditions between Mr and Mrs de Geest, the council and appellants, the Oamaru Whitestone Civic Trust and the New Zealand Historic Places Trust.
That agreement was reached and a final decision has now been released by the Environment Court.
Mr de Geest said yesterday the whole process had cost all the parties involved "an incredible amount of time and money".
But that had not dampened their enthusiasm for the project.
"We were always pretty confident all the way through," he said.
Now they intend to develop detailed working drawings, which is expected to take about 12 months, for the development.
The goal will be to start physical work in 2010.
The final decision issued by the court covers agreement on a landscape plan, preserving public access along the harbour edge, clarifying site boundaries and the term of the lease of the harbour land from the council.
It also provides for title covenants for the apartments prohibiting the keeping of any pets which could harm blue penguins nesting in the harbour area, and ensuring residents will not object to railway, road or port operations.
Judge McElrea said this now resolved all matters which had been raised in the earlier interim decision and confirmed the granting of land-use resource consent for the development.
