Hello,

The eligibility of UPSC is passed graduation in any discipline from a recognized University, there is no minimum aggregate required for this, you can apply even in the final year and you need to be 21 years old.

Now, coming to your question, in UPSC there is optional paper for Philosophy, so in this regard it'll help you a lot, as the syllabus of optional is nothing short of graduation studies, also many toppers have taken this as optional and have qualified successfully, so there is no shortage of study materials as well, but the most important thing is if you like philosophy as a subject or not, if you don't you'll find it difficult to deal with academically or even during preparation of UPSC, as the case is UPSC doesn't discriminate among aspirants, hence people from all backgrounds are allowed to appear for the exam, and this is the sole reason there's no restriction in terms of any particular stream, eventually it's your planning, preparation, dedication and focus that makes one successful as evident from toppers of years who come from different backgrounds such as Engineering, Medical, CA etc.