While some reports put a $3 billion (£2.4 billion) price tag on the agreement, there were no financial details available and both Coca-Cola CEO James Quincey and Mengniu Chief Executive Jeffrey Lu refused to comment on the size of the deal.
Coca-Cola's previous deal ran to 2020 and the new agreement with China's top milk products manufacturer, which will span six Olympic Games, makes it the longest Olympic sponsor, the U.S. drinks maker having first supported the Games in 1928.
"It is a substantial arrangement. It is a profound partnership," said Quincey.
"With Mengniu, we saw an opportunity to expand the dairy aspect of the beverage category.
"We will be activating our own individual marketing plans, but we are pleased to be a joint partner with a well-respected dairy company that is well known to us in China."
The two companies are already working together in some aspects of their business in China.
The announcement is a major boost for the IOC, strengthening its financial future as interest in the world's biggest multi-sports event has waned in the last few years.
Mengniu is the latest Asian company to join as top sponsors after Bridgestone, Toyota and Alibaba in recent years and reflects the region's growing influence of global business.
"This long-term agreement is another demonstration of the relevance and stability of the Olympic Games in these times of uncertainty," IOC President Thomas Bach said.
His organisation will later award the 2026 Winter Olympics to either Milan or Stockholm. Four other cities had pulled out of the bidding, fearful of the Games' cost and size.
Beijing will host the 2022 Olympics, while the Summer Games of 2024 will be staged in Paris. Los Angeles has been awarded the 2028 Olympics.
Mengniu's Lu said the agreement was a key part of their global vision.
"This historic joint partnership deal, together with our global expansion plans, will help Mengniu promote our long-held values around quality and safety," Lu added.
"This is a vital step in our international strategy, and we are honoured to have the opportunity to build the positive reputation of Chinese food and beverage brands among consumers globally."
(Editing by Peter Rutherford)
