Full list of all 39 Titan Quest achievements worth 1,400 gamerscore. It takes around 80-100 hours to unlock all of the achievements in the base game.
The base game contains 24 achievements worth 1,000 Gamerscore, and there are 2 DLC packs containing 15 achievements worth 400 Gamerscore.
Complete the game in Normal mode
Complete the game in Epic mode
Complete the game in Legendary mode
Reach the level 65
Unlock the first mastery
Unlock the second mastery
Defeat the Lernean Hydra (Legendary mode only!)
Defeat the Manticore (Legendary mode only!)
Defeat the Dragon Liche (Legandary mode only!)
Defeat Talos (Legendary mode only!)
Kill 10 monsters
Kill 100 monsters
Kill 1000 monsters
Unlock a mastery completely
Defeat the first Telkine
Defeat the second Telkine
Defeat the third Telkine
Defeat the Titan
Reach 10,000 gold
Reach 100,000 gold
Reach 1,000,000 gold
Finish all the side quests in Greece
Finish all the side quests in Egypt
Finish all the side quests in Orient
Journey north of the Alps
Acquire the mistletoe
Open the ancient gate
Find new friends
Finish the Ragnarok storyline
Improve a legendary item
Have ten different class characters of at least level ten
Defeat King Arganthonios
Defeat The Ancient One
Defeat Ladon
Defeat Tiamat
Defeat Lyktos
Defeat Tartarus on Normal difficulty
Defeat Tartarus on Epic difficulty
Defeat Tartarus on Legendary difficulty