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