The deal is the largest ever overseas acquisition by a Chinese firm, and the second largest in the chemicals industry in the past year.
Read more: Syngenta rises after Monsanto takeover talk
In a statement, Syngenta said ChemChina will pay $465 per share, plus a special dividend to be paid when the deal closes.
The deal came after Syngenta received a $46bn cash-and-stock takeover offer from rival Monsanto, which was rejected last year.
"We will continue to work alongside the management and employees of Syngenta to maintain the company’s leading competitive edge in the global agricultural technology field" ChemChina's chairman Ren Jianxin said.
Meanwhile, Michel Demaré, Syngenta's chairman, said the deal was “focused on growth globally, specifically in China and other emerging markets, and enables long-term investment in innovation”.
This morning Syngenta announced a 17 per cent fall in net income to $1.34bn in 2015. The company blamed low crop prices and currency turmoil for the fall.