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