HTC announced the decision on Wednesday. The pitch, which also involved Maxus Shanghai and local digital agency NIM, was called earlier this year.
The account is reportedly worth US$40 million.
The assignments cover both traditional and digital media. Digitas is responsible for creative and production duties.
Steven Chang, CEO of ZenithOptimedia Greater China, said, "The client liked our committed and passionate team, as well as our proprietary tools in measuring ROI."
Creative materials are currently being adapted from the brand's successful campaigns in the US and Europe.
HTC announced at a press conference in Beijing last month they are planning to launch HTC smartphones in China this year. Creative and PR duties will be pitched later in the year.
London-based shop Moon Design won HTC's separate regional creative pitch, which also took place this summer.
ZenithOptimedia also holds China Mobile's media account in China.