Here is the full list of all 24 Sniper: Ghost Warrior achievements.
Finish the game on Hard difficulty.
Kill 2000 enemies. (Multiplayer)
Complete Act 4.
Finish the game on Easy difficulty.
Finish the game on Normal difficulty.
Kill 250 people using sniper rifle. (Multiplayer)
Kill 500 people using sniper rifle. (Multiplayer)
Collect all secrets.
Kill 250 people using pistol. (Multiplayer)
Win 50 rounds playing online. (Multiplayer)
Complete Act 3.
Complete Act 2.
Kill a total of 30 enemies with Browning gun.
Shoot 5 cable lines using sniper rifles.
Deliver 100 headshots.
Kill all enemies attacking your pontoon from the riverside on 'Weaken The Regime' level.
Complete Act 1.
Deliver 50 headshots.
Shoot an enemy through a wall.
Kill 15 enemy using concentration mode.
Kill 2 enemy with one shot.
Kill 2 enemy with one grenade.
Kill 10 enemies with throwing knives.
Kill 10 birds.