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