If you really want to get into the weeds of its creation, the best overall book is Mohamed I. Shaker, The Nuclear Non-proliferation Treaty: Origin and Implementation, 1959-1979 (Oceana Publication, 1980), in 3 volumes, easily available online. It is detailed to the point of being kind of unbearably dull at times (I find any detailed account of UN treaties to be pretty dull, if I am honest, because they end up being very dry accounts of many very dry meetings and pre-meetings and so on, all of which are kind of stilted in that formal UN way), but the overall thread is actually quite interesting if you get beyond that (he does a great job of getting at what different delegations found difficult about crafting and selling the NPT, and really makes it NOT feel like a foregone conclusion). I used this, many years back, to create an "NPT Simulation" exercise for my classes, as an aside, where students have to represent positions of different groups that were involved in the early NPT talks; it was a super useful book for that purpose.

I am honestly not sure what I would recommend as something for its impact — it's a broad topic, and ties deeply into the history of non-proliferation and proliferation. There are about a million articles by scholars debating its value and worth, but all of these are somewhat hampered by the fact that they rely on the counterfactual of "what if the NPT hadn't been signed?" which is of course hard to know, and so people project their preconception (usually whether they are for or against arms control, which divides in complex ways politically — many disarmament proponents, for example, don't think the NPT is very good because it enshrines a world of nuclear "haves" and "have nots" and has not lead to disarmament) into their analysis.

If it is not obvious, I would say: for many years I have thought that there is a real opportunity out there for someone to write a new history of the NPT, because the existing stuff is just not that compelling (even if Shaker's work is very detailed). But to my knowledge it does not yet exist. (And I don't think I am going to write that book... I don't have the heart to work on UN-related things because they are so terminally bureaucratic and dull.)