True said on Monday that the investment by the state-owned Chinese company is part of a 65-billion-baht share issue that will mainly be used to reduce True's debt.
True, which has mobile telephone, cable TV and internet businesses, said it will sell about 4.4 billion new shares to China Mobile for $880 million. It will offer existing shareholders more than 5.6 billion new shares at the same price paid by China Mobile of 6.45 baht a share.
China Mobile is the world's largest mobile phone company by subscribers but has a limited presence outside of mainland China. It had 785 million subscribers in China as of April 30.
Thailand's second coup in eight years has ushered in relative stability after six months of protests in Bangkok against the elected government and political violence that killed 28 people.
The economy shrank in the first quarter as the political uncertainty took a toll on spending by consumers and businesses.
True Corp is majority owned by Thai billionaire Dhanin Chearavanont's Charoen Pokphand Group.
Mr Dhanin last year bought a 15.6% stake in China's Ping An Insurance for $7.4 billion.
True said the share sale should be completed by the end of August. Its shares rose 2.8% on Monday to 7.45 baht.