Either your opponent will have to lose life or you will have to gain life to start the process. Then, yes, unless someone does something to stop it, you'll enter a loop which will win you the game.
As hinted above, there are numerous effects that can change the outcome. If an opponent controls Platinum Angel, if they cast Angel's Grace, or if you control Abyssal Persecutor, the game will enter into a loop of mandatory actions which will end the game in a draw. If an opponent has hexproof or shroud for some reason (e.g. Witchbane Orb, True Believer), Sanguine Bond won't be able to target him or her and the loop will terminate. Voidslime can end the loop (but doesn't prevent from being restarted later).