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