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