The project is part of China's huge regional infrastructure plan to build a high-speed rail network connecting the southern city of Kunming with Laos, Thailand, Malaysia and Singapore.
Construction has already begun in Laos but the Thai segment of rail has been stymied for years by tussles over financing, loan terms and protective labour regulations in the Southeast Asian kingdom.
The funding approval from Thailand's cabinet came after junta chief Prayut Chan-O-Cha invoked his absolute powers last month to clear a series of legal and technical hurdles standing in the way of the deal.
The first stage of the high-speed line will run 250 kilometres (150 miles) between Bangkok and the northeastern province of Nakhon Ratchasima, also known as Korat.
More From This Section
The plan is to then extend the track to Nong Khai on the border with Laos.
Thailand will cover the construction costs but the vast majority of technical expertise will come from Chinese engineers - something that has disgruntled local firms who were angered by Prayut's decision to loosen restrictions placed on foreign engineers.
The rail deal is one of the biggest foreign investment projects in Thailand in years and is part of Beijing's 'One Belt, One Road' infrastructure drive which aims to revive ancient Silk Road trading routes.
China's largesse and increased investment presence in Asia comes as rival power the United States becomes more isolationist under President Donald Trump.
Thailand's junta has cosied up to Beijing since its 2014 power grab, shelling out billions on Chinese arms and welcoming investment from the regional superpower.