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