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