Here is the full list of all 24 Sniper: Ghost Warrior achievements.
Kill 500 people using sniper rifle. (Multiplayer)
Win 50 rounds playing online. (Multiplayer)
Kill 250 people using sniper rifle. (Multiplayer)
Collect all secrets.
Complete Act 4.
Finish the game on Normal difficulty.
Finish the game on Hard difficulty.
Finish the game on Easy difficulty.
Complete Act 3.
Kill a total of 30 enemies with Browning gun.
Shoot 5 cable lines using sniper rifles.
Complete Act 2.
Kill 10 birds.
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.
Kill 10 enemies with throwing knives.
Deliver 50 headshots.
Kill 2 enemy with one shot.
Kill 15 enemy using concentration mode.
Shoot an enemy through a wall.
Kill 250 people using pistol. (Multiplayer)
Kill 2000 enemies. (Multiplayer)