Here is the full list of all 24 Sniper: Ghost Warrior achievements.
Collect all secrets.
Finish the game on Normal difficulty.
Finish the game on Hard difficulty.
Kill 15 enemy using concentration mode.
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)
Complete Act 4.
Finish the game on Easy difficulty.
Kill 2 enemy with one grenade.
Complete Act 3.
Kill a total of 30 enemies with Browning gun.
Complete Act 2.
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.
Kill 10 enemies with throwing knives.
Kill 10 birds.
Deliver 50 headshots.
Shoot an enemy through a wall.
Kill 2 enemy with one shot.