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