I think you want Machiavellian

according to the Collins Dictionary (UK edition)

Machiavelli Niccolo - 1469-1527, Florentine Statesman and political philosopher, secretary to the war council of the Florentine republic (1498-1512). His most famous work is "Il Principe" (The Prince 1532).

Machiavellian (also spelt Machivelian), sometimes not capitalised
adj.
1. of or relating to the alleged political principles of Machiavelli; cunning, amoral and opportunist
2. a cunning, amoral and opportunist person, esp a politician

We usually attribute the idea that "the means always justifies the end" to Machiavelli but judging by the definition above, either a) that is a gross simplification of what he said/did or b) the Collins Dictionary is hedging its bets in case his descendants sue for libel.