The best political philosophy books all circle one question: who gets to give orders, and what a citizen owes the state that claims the right to give them. The real decision is not which thinker turns out to be right, it is which century you want to start in. Some of these were written to defend a government and some to bring one down, and they answer each other across three hundred years.
A Theory of Justice is the pick to own if you want the argument that modern political theory still runs on, and it rewards a reader willing to go slowly. Anyone who would rather begin with the original questions about rule and citizenship should open Aristotle's Politics first.
Political philosophy divides into primary texts that made an argument and later books that explain those texts, and the ten below are all the former. Ancient civic theory, seventeenth-century sovereignty, the quarrel over the French Revolution, industrial-age critique and the modern fight about fairness each get the book that started them.