It depends! Typical lawyer answer.
Trademark rights are jurisdictional, meaning that just because you have rights in one jurisdiction, like the U.S., doesn’t mean you have rights in another jurisdiction, like Canada, the EU, China, or anywhere else for that matter. The rules for how long a trademark registration will be valid vary by jurisdiction.
Here in the U.S., federal (there are also state trademark rights) trademark rights are based on use; in other words, if you use a trademark in interstate commerce (generally, this means across state lines, although there are exceptions) to offer and sell a product or service. Without formal registration of your trademark, if you actually use your unregistered mark in interstate commerce you have what are called “Common Law” rights in your trademark. However, you will not receive all the valuable benefits of the federal Lanham Act, the law governing federal U.S. trademarks, unless you formally apply for registration or your trademark and are granted a Registration Certificate by the United States Patent and Trademark Office (the “USPTO”).
In the United States, a trademark registration can last forever, so long as you continuously use the mark in commerce and certain maintenance and renewal deadlines are met and required filings are completed. For example, in the U.S., a trademark registration must be renewed between the 5th and 6th year after registration, between the 9th and 10th year after registration, and every 10 years thereafter. Failure to file the appropriate renewal documents with the USPTO will result in the registration being cancelled. If this happens you may still have Common Law rights, but you will lose all the Lanham Act statutory benefits granted by registration. Most countries have a similar renewal system, although the timing and requirements may be different.