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