The plugin will not be enabled by default. To enable it in the current project, go to "File→Settings...→google-java-format Settings" and check the "Enable" checkbox.

To enable it by default in new projects, use "File→Other Settings→Default Settings...".

1. Build google-java-format*all-deps.jar by running mvn install in the core directory.
2. Create a new "IntelliJ Platform Plugin" project.
3. Add the google-java-format.iml module to this project by doing File→New→Module from Existing Sources... and selecting the iml file.
4. Under "File→Project Structure→Libraries" add core/target/google-java-format*all-deps.jar file. IntelliJ will ask if you want to add it as a dependency to the google-java-format module. You do.