How to disable Maven auto import automatically in IntelliJ IDEA?

Uncheck Project Settings | Maven | Importing | Import Maven projects automatically.

For IDEA 14+ it's under Settings | Build, Execution, Deployment | Build Tools | Maven | Importing | Import Maven projects automatically.

For IDEA 2020+, open Settings | Build, Execution, Deployment | Build Tools and check "Reload projects after changes in the build scripts" and "Any changes"

Although above answers are correct. I have observed that above option is not available on IntelliJ 2020.2 version. So, there you need to go Settings -> Build Tool -> Check "Reload projects after changes in the build scripts" -> check "Any changes"