WA Premier Colin Barnett and Regional Development Minister Brendon Grylls confirmed the deal on Tuesday, after widespread reports last week that the Chinese bid had beaten Australian Agricultural Company (AACo), which wanted the land to grow cotton.
Mr Barnett said the deal, which was done with the input and cooperation of the local Miriuwung and Gajerrong people, was a pioneering move.
"Western Australia is 20 years ahead of the rest of the country in our engagement with Asia and particularly China," Mr Barnett said.
"I think it will be the forerunner of more overseas investment, particularly from China, into the agricultural industry.
"This is one spectacular way of diversifying our economy and developing the north of the state."
Mr Grylls was coy when asked what KAI was likely to pay for the lease in the Goomig and Knox Plain areas, with commercial negotiations to take several more months.
"The rent on pastoral country is not the same as a fully fledged farm. It will be a commercial rent, and the valuer-general will be give us his advice on what that is worth," Mr Grylls said.
"But remember we are looking to attract a $700 million investment, and this land will be retained in ownership by the people of Western Australia."
With federal Special Minister of State Gary Gray looking on, KAI chief executive JianZhong Yin said there were still challenges to overcome in WA and the company had a firm eye on expansion into the Northern Territory.
"There are still significant challenges ahead to develop this project to its full potential and achieve the economies scale KAI requires for this to be commercially viable," Mr Yin said.
"But we have the skill set to overcome the many challenges this project represents."
Edna O'Malley, chairwoman of the Miriuwung Gajerrong Corporation, said the flow of jobs and training for local people would be invaluable.
"We had the American farmers coming through on Ord Stage 1 and were not consulted," Ms O'Malley said.
"On this project we have got now, we are a partner with them and with the government.
"It is a big step for us.
"We have never done this partnership in Australia before with the indigenous people, and with development and farming - this is a new path we are taking, and I believe it is a good one."
- AAP