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