Google bought the company at $12.5bn less than two years ago.
Lenovo plans to build up its smartphone unit through the Motorola purchase, which may help offset its slowing personal computer business.
Google will keep the majority of Motorola’s lucrative patents, which include one for Android software.
In a statement, Google said the smartphone market was “super competitive” and that Motorola would “be better served by Lenovo”.
The purchase is set to make Lenovo the world’s third-largest smartphone maker behind Samsung and Apple, and will give the Chinese vendor gets access to the valuable US smartphone market and the fast-growing Latin America region.
This complements its existing global PC business.