Here is the full list of all 24 Sniper: Ghost Warrior achievements.
Collect all secrets.
Kill 10 birds.
Complete Act 4.
Finish the game on Easy difficulty.
Finish the game on Normal difficulty.
Kill 10 enemies with throwing knives.
Complete Act 3.
Complete Act 2.
Kill a total of 30 enemies with Browning gun.
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 grenade.
Deliver 100 headshots.
Deliver 50 headshots.
Kill 2 enemy with one shot.
Kill 15 enemy using concentration mode.
Shoot an enemy through a wall.
Finish the game on Hard difficulty.
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)