The LG G3 can now root successfully with one click-rooting tool called “Stump Root”. This tool supports all US variants of LG G3 (D850, D851, LS990, VS985) including the troublesome Sprint variants and very simple to use. Here is how to use Stump Root app to root your LG G3.
Stump Root is a one-click rooting tool, which means simply by hitting a button will root your phone. For Android fans, there is no need to say about the benefits of root. You will get “admin” access to your phone, it enables you to run apps that are more powerful and install custom ROMs.
How to Root LG G3 (D850, D851, LS990, VS985)
1. On your phone, go to Settings -> Security -> and enable “Unknown sources”.
2. Download “Stump root” tool and copy it to your phone. (Download from this XDA thread)
3. Install “Stump.apk” just like any APK file.
4. Run the Stump app and tap on “Grind”.
5. When it says “Reboot to root”, reboot your phone.
6. Once rebooted, install SuperSU from the Play Store.
That is it! Your LG G3 is now completely rooted. Enjoy admin access on your phone (source)
Note: For international variants of LG G3 (D851, D852, D855, D855K, D855P, D5850, F400K, F400L, F400S), users can use PurpleDrake app. You will get more details from this XDA thread.