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