The federal regulator ruled Tuesday the deal was unlikely to reduce competition "due to, among other things, the existence of a large number of competitors and the low barriers to entry in the fast food industry."
Burger King has offered US$11 billion for the Canadian coffee chain.
The deal still faces a review under the Investment Canada Act and requires approval by Tim Hortons shareholders.
Burger King and Tim Hortons announced the deal in August.
The combination of the two companies would create the world's third-largest quick service restaurant company, with about $23 billion in system sales and more than 18,000 restaurants in 100 countries.
Also on HuffPost