Federal cabinet is expected to meet on Tuesday to approve Badgerys Creek as the location of Sydney's second airport.
Fairfax Media has learnt the senior ministers who matter have come to a decision on the site, making cabinet's tick-off all but a foregone conclusion.
The decision to go with Badgerys Creek ends months of speculation and will spur hundreds of millions of dollars of new investment in Sydney's west and lead to thousands of new and ongoing jobs.
The project is also regarded as important to the national economy.
The announcement has been positioned as the first step, with the details of the infrastructure that will support the site still to be hammered out.
The federal and NSW governments are working closely together on the infrastructure package, expected to be worth hundreds of millions of dollars and to generate thousands of jobs.
But a critical aspect will be the funding quantum after an initial package of $300 million was rejected by the NSW government as inadequate.
The details of the funding package for related infrastructure to support the airport may be held back until the federal budget is handed down in May. The announcement of the site may allow work to begin on infrastructure upgrades, such as roads around the airport, and it will also trigger the process in which Sydney Airport will be given first right of refusal to build the new airport.
Tuesday's cabinet meeting will consider other key aspects of the federal budget, now just a month away, given Treasurer Joe Hockey and Prime Minister Tony Abbott have only both arrived back in the country in the past two days.
Western Sydney Liberal MPs and the NSW government have been kept informed about the airport decision-making progress but most were remaining tight-lipped ahead of the meeting.
The decision as to the location of the second Sydney airport has caused enormous political pain, with both sides reluctant to finally commit for fear of sparking a major scare campaign in marginal seats before the next election, based on expected traffic increase, construction dislocation lasting years and increased aircraft noise.
The Badgerys Creek site in south-west Sydney was purchased for an airport between 1986 and 1991, but has sat largely unused since then, as politicians have been unable to commit to the project.
Labor transport spokesman Anthony Albanese has offered bipartisan support to the government on the decision, based on the logic that the political gridlock had lasted years and threatened to delay a final decision indefinitely.
He said the discussion and feasibility studies had dragged on for years and a decision was needed now to guarantee that demand could be met.
"You won't see from me politics being played on this issue because it is a national economic interest issue," Mr Albanese had said.
"I've made it clear, even when I was [transport] minister, that I thought construction should commence in this term," he said.
"And that is what I support the government doing."
But even some on his own side quickly dismissed that suggestion, with Chifley MP Ed Husic making his continued opposition to the Badgerys Creek location known.
Even the state government has been undecided amid fear, bordering on terror, in the political community that whichever site was chosen would cause major local opposition resulting in a backlash at the polls.
Earlier this month, Transport Minister and Deputy Prime Minister Warren Truss said the government was eager to reassure affected communities before a decision was made.
"Every place in the world with a population of 2-to-4 million has an airport and they need that for local and domestic uses. So the key thing for any new airport in western Sydney will be the provision of services to the immediate neighbourhood, to the people who live there," he had said.
"There are two million people or more living in the western Sydney basin, that number is likely to double over the years ahead and therefore that area is going to need substantial infrastructure."
He predicted Sydney Airport would remain the prime gateway to Sydney "for the foreseeable future but there is substantial population expansion in all corners of Sydney and those people will need the full range of transport services and facilities for their needs as well".
Mr Truss said the government was consulting with federal and state MPs based in Sydney's west about the plan.
On Monday night, most of those Western Sydney MPs were keeping their own counsel about the airport but it is believed not all are happy with the outcome, because it will expose them to serious local opposition come the next election.
Work on the airport could begin by the end of this year but it is understood that it will take about a decade to be built, with thousands of jobs to be created while construction is underway.
The airport is expected to have just a single runway when flights begin in the mid-2020s.
Over time, the airport is expected to create tens of thousands of jobs for western Sydney.
Mr Abbott used some of his time in China in the past week to discuss the situation with NSW Premier Barry O'Farrell who, with other state premiers, went along to China for the ride.