1. Before you can publish your plugin code to mavenLocal(), you have to add add the ‘maven-publish’ to your plugin build.gradle.

plugins {
    id 'java-gradle-plugin'
    id 'maven-publish'
    ...
}

2. Then publish you artifacts to mavenLocal()

$ gradlew publishToMavenLocal

3. In your application code add mavenLocal() to the pluginManagement of your settings.gradle file.

pluginManagement {
    repositories {
        mavenLocal()
        gradlePluginPortal()
    }
}

4. Now you can reach your plugin in your application build.gradle from maven local repository :)

plugins {
    id '<myplugin-id>' version '<myplugin-version>'
}

A Working example on github

1. Example Plugin
2. Example Application Code

$ git clone https://github.com/elmolm/gradle-playground.git
$ cd extended-java-library-plugin
$ gradlew publishToMavenLocal
$ cd ../mavenlocal-plugin-resolve
$ gradlew check