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