The NSW Government confirmed the $11.5 billion (2012 dollars) project will be built in three stages with the M4 widening to start first and be completed in 2017.
WestConnex is the largest infrastructure project in Australia, linking western and south Western Sydney with the city, airport and port in a 33 kilometre continuous motorway.
NSW Premier and Minister for Western Sydney Barry O’Farrell said WestConnex would ease congestion, deliver liveable and connected communities and create jobs across Sydney.
"WestConnex is a game-changer for Sydney – it will save motorists time by making travel between Sydney’s west and the east easier,” said Mr O’Farrell, who was joined at the announcement by Prime Minister Tony Abbott and Deputy Prime Minister Warren Truss.
"This delivers on our election commitment and means relief is now in sight for Western Sydney motorists.
"WestConnex will help motorists avoid up to 52 sets of traffic lights, creating a saving of 40 minutes on a trip from Parramatta to Sydney Airport and halving the travel time from Parramatta to the CBD to 25 minutes.
"WestConnex will inject $20 billion into the NSW economy including 10,000 construction jobs and hundreds of apprenticeships for young people.
"Our commitment to WestConnex, and our major public transport infrastructure projects like the North West and South West Rail Links, and light rail, shows we’re serious about transforming Sydney for the better."
Mr Gay said WestConnex will remove up to 3,000 trucks a day from Parramatta Road and put them in underground tunnels, returning the surface roads and land uses to local communities.
"This will enable urban revitalisation to occur along the 20 km long corridor between Broadway and Parramatta, creating new jobs, stimulating productivity and delivering new homes in this key growth area of Sydney," Mr Gay said.
"This is similar to the revitalisation of Surry Hills and parts of Redfern following the construction of the Eastern Distributor.
"I'm delighted the next step in delivering this project happens today with the lodging of the planning application with the Department of Planning & Infrastructure for an environmental assessment of Stage 1," he said.
"The next stage of the project will also involve consultation with industry to explore innovative financing and engineering solutions. The first industry session will occur this week.
“This industry engagement approach will build on the success of the North West Rail Link consultation, and will ensure a value-for-money solution for motorists and taxpayers."
The NSW Government is providing $1.8 billion for WestConnex while the new Australian Government has committed $1.5 billion over four years.