Here is the full list of all 37 THIEF achievements worth 1,000 gamerscore. It takes around 40-50 hours to unlock all of the achievements on Xbox 360.
Scored an epic 5,000,000 or more in a Challenge Map
Used 40,000 gold
Completed 25 optional Thieving Objectives
Completed all client jobs in The City
Completed all collectible sets
Completed 10 optional Thieving Objectives
Completed all Basso Jobs in The City
Discovered all secret areas
Finished the game in 15 hours or more
Completed a collectible set
Picked 100 pockets in a single playthrough
Disarmed ten trap mechanisms
Shot a bottle in mid-air with an arrow
Discovered 15 secret areas
Picked a pocket and a lock using the focus ability
Stole all loot and collectibles in a single chapter.
Finished the game on Master difficulty
Finished the game with a custom difficulty of 700 points or more
Finished the game without a single kill or knockout
Finished Chapter Eight
Reached the final chapter without using the focus ability
Finished Chapter Seven
Finished Chapter Six
Finished Chapter Five
Found all the secret stashes in Moira
Finished Chapter Four
Finished Chapter Three
Killed or knocked out 10 people using the environment
Finished Chapter Two
Finished 3 consecutive chapters without taking damage
Sweet sixteen. Snuff said.
Finished Chapter One
Finished a single chapter without alerting anyone
Uncovered Lyegrove's secret
Stole 5 collectibles
Picked a lock with masterful speed
Finished the Prologue