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 pistol. (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.
Kill 10 birds.
Complete Act 3.
Shoot 5 cable lines using sniper rifles.
Deliver 100 headshots.
Complete Act 2.
Kill a total of 30 enemies with Browning gun.
Kill 10 enemies with throwing knives.
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.
Kill 2 enemy with one shot.
Deliver 50 headshots.
Kill 15 enemy using concentration mode.