Important:
Back up important files stored on your device before proceeding with the steps so that in case something goes wrong you will still have your backed up files.
Disclaimer:
This site or the developers are not responsible if you damage or brick your device.Do it at your own risk and follow the instructions correctly.
Requirements:
First, make sure that you have the Marshmallow Update on LG G3 installed and running
What you need for this is a custom recovery like TWRP recovery, or Cyanogen recovery. Download the TWRP Recovery for LG G3 model no. D855 here.
Root LG G3 D855 official Android 6.0 firmware Marshmallow 30B
Download SuperSU Root package.
1- If you have installed TWRP Recovery, download the file SuperSU from above, and install it using TWRP recovery.
2 For that, SuperSU move the file to your device, and then reboot into recovery mode TWRP recovery.
3- Once in TWRP, tap the Install button, then select to confirm the zip file and then do the swipe action at the bottom to confirm.
4 When finished, tap the "Reboot System" button to restart the device.
That all. Your LG G3 will be rooted successfully.