Mr Barnett said the Gorgon project, which commenced construction in 2009, was one of the most ambitious projects ever undertaken in Australia.
"The project is the largest single resources project in Australian history, and is also one of the largest natural gas projects in the world," he said.
"To date, more than A$34 billion has been invested within the State and Australia, and 455 contracts have been awarded to Western Australian companies for goods and services."
The Premier said the project would continue to generate economic benefits for WA over the next few decades.
"As the project moves into production, its longstanding benefits include operational and maintenance jobs, the provision of domestic gas and the payment of State taxes," he said.
Chevron Australia estimated that the project had created more than 10,000 jobs across the nation during construction - the majority of which were created in WA.
The Gorgon Project also includes one of the world's largest carbon dioxide injection projects, which will reduce the overall greenhouse gas emissions by about 40 per cent.
"From its immense scale through to its location on Barrow Island - a Class A Nature Reserve - protecting people and the environment has been fundamental in the construction of Gorgon. Working together, the State Government and the joint venture partners have managed to ensure Barrow Island's environmental integrity has been maintained through strict quarantine conditions," Mr Barnett said.
"I congratulate Chevron Australia and its joint venture partners on this important milestone, and look forward to seeing the benefits of this project flow through the Western Australian economy for decades to come."
The Gorgon Project is a joint venture between the Australian subsidiaries of Chevron, ExxonMobil, Shell, Osaka Gas, Tokyo Gas and Chubu Electric Power
The project includes a three-train, 15.6 million tonne per annum LNG plant, domestic gas plant, 4.2km loading jetty and offloading fPrmeieracility, carbon dioxide injection project, workforce accommodation and administration buildings, and offshore infrastructure
The Gorgon Project started construction in December 2009