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