Here is the full list of all 66 Torchlight achievements. It takes around 100-120 hours to unlock all of the achievements on Windows.
Drink 5,000 potions
Kill 25 champion trolls
Sell 10,000 items to vendors
10 mods used at the same time
Retire a character
Defeat Ordrak with no deaths
Defeat Ordrak on Easy Hardcore
Defeat Ordrak in 8 hours or less
Defeat Ordrak in less than 5 hours
Suffer 20 disenchants from the enchanter
5 mods installed at the same time
Kill 50,000 monsters
1 game mod installed
Beat the game with all three classes
Defeat Ordrak on Very Hard
Achieve player level 100
Catch 1000 fish
Reach the 50th floor of a dungeon
Complete 200 Quests
Gamble 100 times
Achieve maximum fame
Complete 25 Gar Quests
Smash 1500 Breakables
Gamble 50 times
Achieve player level 65
Achieved enlightenment by speaking with the horse 100 times
Successfully enchant one item 10 times
Gamble a unique item
Permanently transform your pet
Transform your pet into a Mimic
Gamble 20 times
Do at least 10,000 damage to an enemy in a single strike
Defeat Ordrak on Easy or Normal
Defeat Ordrak on Hard
Defeat Alric
Collect 250,000 gold
Defeat Medea
Have an item disenchanted on the first enchantment attempt
Successfully enchant one item 5 times
Defeat Krag
Have 100,000 gold in your inventory
Successfully create 25 items using the transmuter
Use 50 potions on your pet
Kill 5000 Monsters
Defeat the Ember Colossus
Take 25,000 steps
Defeat the Root Golem
Catch 100 fish
Pull 100 levers
Defeat the Overseer
Catch 50 fish
Fill your pet's inventory
Change your pet by feeding it fish
Equip a spell on your pet
Defeat Brink
Blow 25 enemies to pieces with critical strikes
Send your pet to town
Find the entrance to the mine
Reach level 100
Complete 50 Hatch Quests
Retire two characters
Retire over 300 levels worth of characters
Die 500 times
Defeat Ordrak on Normal Hardcore
Defeat Ordrak on Hard Hardcore
Defeat Ordrak on Very Hard Hardcore