Here is the full list of all 24 Sniper: Ghost Warrior achievements.
Win 50 rounds playing online. (Multiplayer)
Kill 2000 enemies. (Multiplayer)
Kill 250 people using pistol. (Multiplayer)
Kill 500 people using sniper rifle. (Multiplayer)
Kill 250 people using sniper rifle. (Multiplayer)
Complete Act 4.
Finish the game on Easy difficulty.
Finish the game on Normal difficulty.
Finish the game on Hard difficulty.
Collect all secrets.
Complete Act 3.
Shoot 5 cable lines using sniper rifles.
Complete Act 2.
Kill a total of 30 enemies with Browning gun.
Kill 10 birds.
Kill all enemies attacking your pontoon from the riverside on 'Weaken The Regime' level.
Deliver 100 headshots.
Complete Act 1.
Deliver 50 headshots.
Kill 2 enemy with one grenade.
Kill 10 enemies with throwing knives.
Kill 2 enemy with one shot.
Kill 15 enemy using concentration mode.
Shoot an enemy through a wall.