Is there a way to to fire some code before user validation? Am wondering if there is a way to fire some code prior to user validation being actioned? I have code running in a plugin that fire onBeforeSave but validation is actioned before this. So was wondering if there is a function that can be run onBeforeValidation specifically for users.

Cheers
Currently Craft doesn't have any events related to validation.  You can see the full list of events available here.

You can always add it as a feature request, though. Be sure and add examples of your specific use-case.