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