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