
Download and install the HTC mobile phone drivers. See below "HTCDriver3.0.0.007.exe".
Download the "root-one-x.zip" file below.
Extract root.zip into a directory on your computer.
Plug your HTC One X into your computer via USB. Recommended: Plug your device’s USB cable into the back of your computer if you’re using a desktop PC.
Enable USB Debugging on your HTC One X. Settings >> Developer Options >>USB debugging (checked)
Double click root.bat/root-linux.sh/root-mac.sh to run the script.
Congratulations! Your device will reboot a number of times and then you will have full root access.
Thanks to Briefmobile for these instructions.