Here is the full list of all 24 Sniper: Ghost Warrior achievements.
Complete Act 4.
Finish the game on Easy difficulty.
Finish the game on Normal difficulty.
Finish the game on Hard difficulty.
Collect all secrets.
Complete Act 3.
Kill 2000 enemies. (Multiplayer)
Win 50 rounds playing online. (Multiplayer)
Kill 250 people using pistol. (Multiplayer)
Kill 250 people using sniper rifle. (Multiplayer)
Kill 500 people using sniper rifle. (Multiplayer)
Kill 2 enemy with one shot.
Complete Act 2.
Kill a total of 30 enemies with Browning gun.
Shoot 5 cable lines using sniper rifles.
Deliver 100 headshots.
Kill all enemies attacking your pontoon from the riverside on 'Weaken The Regime' level.
Complete Act 1.
Kill 2 enemy with one grenade.
Kill 10 enemies with throwing knives.
Deliver 50 headshots.
Kill 10 birds.
Kill 15 enemy using concentration mode.
Shoot an enemy through a wall.