How do you defeat Zant in Zelda Twilight Princess?

Answer 1

Zant will fight you in a series of stages, each of which will be reminiscent of a previous boss/sub-boss fight.
First, he'll fight you in the boss room of the Forest Temple. Dodge his blasts and throw your Gale Boomerang at him to bring him to the shore so you can hack & slash a bit. If you have the Great Spin (last hidden move) you usually need to bring him to the shore once.
Next, Zant will change the arena to where you fought the Goron sub-boss in the Goron Mines. You really don't need to use the Iron Boots to hang on, just keep running the opposite way of Zant while he's ground-poundin' everywhere. After that he'll try to blast you again, these can be hard to dodge but don't sweat it if you take a hit or two. After blasting, he'll be tuckered out, this is your chance to run in and score some hits.
Next arena will be from the Lakebed Temple, in the lair of Morhpeel. Immediately put on your Zora Armor and Iron Boots. Four gigantic Zant Heads will appear and Zant will be hiding in one. He'll try to blast you, then wait a few seconds before disappearing and coming back. Clawshot him to pull him out of his Head and slash him a few times. Rinse and repeat and in no time, you're back in the Forest Temple.
This part puts you in the crazy booty shaking baboon's room. Zant will hop around on the pillars. Follow him around and dodge when he tries to blast you. Right after he finishes blasting he'll be tuckered out (yes AGAIN) and you can roll into the pillar and knock him off. Then hack away and soon enough, you're moving on into the next part.
Now you're in the master bedroom in the Snowpeak Ruins. Remember how you have to smash Blizzeta with the Ball & Chain to get rid of her armor? Well, now that applies for Zant. Well, sort of. Hit him in the foot with the Ball & Chain and he'll hop around in pain, shrinking as he goes, until you catch up and deliver some well-deserved sword blows. You may have to Ball & Chain him twice to finish this part. Hold on, you're almost done.....
The final arena is the only new one; directly in front of the Twilit Hyrule Castle. This time, Zant's not fooling around as he brandishes double swords on you. When he comes at you swinging both like a madman, just block until he stops then strike back. Eventually he'll start spinnning like a top and ram into you. You can't block this one, so you'll have to dodge it. Also, keep away from the walls here, as touching them will throw you into the arena and damage you. This is where all those Hidden Moves finally become really useful. Basically, block and dodge until you get a chance to go in for some hits, and Zant will go down (for good this time), in no time.
Hope it helps, sorry so long.

PS: in the last part, the Back Slice works pretty well.

Answer 2

First use your Gale boomerang to bring Zant toward you and slash him with your sword.