Full list of all 54 The First Templar achievements worth 1,250 gamerscore. It takes around 20-25 hours to unlock all of the achievements in the base game.
The base game contains 48 achievements worth 1,000 Gamerscore, and there is 1 DLC pack containing 6 achievements worth 250 Gamerscore.
Performed 50 stealth kills
Healed your partner
Survived the events of Friday the 13th
Set 50 objects on fire
Successfully tracked 20 trails to their end
Defeated Muzafar
Won a duel
Advance a character to 5 Zeal Orbs
Killed an enemy grabbed by the other character
Finished 30 fallen enemies
Survived the siege of Acre
Stealth killed a noise distracted enemy
Killed an enemy by knocking him from a ledge
Rescued Marie d'Ibelin
Advanced a character to 5 Health Orbs
Smashed 5 enemy shields
Killed all opposing squads with a siege weapon
Destroyed a breakable wall
Discovered with a clue
Disarmed a bear trap
Defeated the Beast
Used the "Revive" action to help your teammate
Finished a whole level without both characters dropping below 1 Health Orb
Completed all Bonus Objectives in a single level
Rescued the messenger of King Philip
Discovered all chests in a single level
Killed 5 enemies in less than a minute without taking damage
Explore the Temple of the Nine
Find the Grail
Complete all levels on Casual or higher difficulty
Complete all levels on Normal or higher difficulty
Complete all levels on Hard difficulty
Complete all Bonus Objectives on all levels
Collect all Templar Chronicles
Find all collectible outfits in the game
Find all collectible weapons in the game
Save your partner from a dog attack
Succesfully perform 10 countermoves
Kill 20 enemies with a ranged attack
A fleeing enemy is killed with a siege weapon by you or your partner
Acquire all Charge skills for Celian
Acquire all Dagger throw skills for Marie
Hit 4 enemies with your charge attack at the same time
Hit 4 enemies at the same time with your All-around Attack.
Play an online multiplayer game with one of you Xbox LIVE friends
Finish a level in an online multiplayer game
Finish all levels in the campaign in multiplayer online mode
Complete 5 levels in online multiplayer with different partners
Complete the Arena
Complete all Bonus Objectives in the Arena
Kill 15 opponents in the Arena using Cyclone Strike.
Complete the first round in the Arena without taking damage
Complete the second round in the Arena without taking damage
Complete the third round in the Arena without taking damage