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