Ok... I'm making a Paladin of Conquest from Xanathar's Guide to Everything. At around 9th level I want to Multiclass three levels into a Hexblade Warlock (also from XGtE). I was wondering does having prior levels before Warlock affect some of the Eldritch Invocations that might have Level Prerequisites (such as the Lifedrinker and Thirsting Blade Invocations)? As in am I able to select them for having the total Character Levels or does it only count towards Warlock Class levels?
Only your Warlock class matters for the prerequisites.
In your study of occult lore, you have unearthed eldritch invocations, fragments of forbidden knowledge that imbue you with an abiding magical ability. A level prerequisite refers to your level in this class.
Other things, like Cantrips and Proficiency Bonuses, are based on your overall character level, but not Invocations.