In exchange for the Uber China assets, Uber and its Chinese partners will receive shares equivalent to 20 per cent of Didi Chuxing, a statement said.
The combined Chinese firm will be valued at USD 35 billion, Bloomberg News reported.
Since Uber launched its China operations little more than two years ago both companies have spent billions of dollars on subsidies for drivers and passengers in China, as well as trading vitriolic accusations, as they fought for dominance in the potentially lucrative market.
In the Didi statement Cheng said the two firms "have learned a great deal from each other over the past two years in China's burgeoning new economy".
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Earlier this year Uber said it lost USD 1 billion annually in China, and Didi was thought to be dropping similar amounts of money.
A lengthy post on Kalanick's verified Facebook page today called Uber's battle in China a "big, bold idea" and "one of the most rewarding experiences I've had as an entrepreneur".
His at times elegiac farewell praised the company's China team as "the smartest and most entrepreneurial sons and daughters of China" who were "nobly serving" China's cities.
But he went on: "As an entrepreneur, I've learned that being successful is about listening to your head as much as following your heart."
A sustainable business was "only possible with profitability", he said, and the merger would free up "substantial resources".
The deal comes days after Chinese authorities announced new rules governing ride-sharing, making clear for the first time that they may operate legally in the country.
The new rules will also forbid ride-sharing platforms from operating below cost, possibly restricting their scope to offer subsidies.
Rides in major cities with Uber and Didi have often cost significantly less than regular cab fares due to the subsidies, and many drivers work for both companies at the same time.
One Didi driver was reluctant to believe the news of the merger today. "If it is true, the allowance offered by Didi or Uber now will certainly decrease." the man, surnamed Su, told AFP.