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