Here is the full list of all 24 Sniper: Ghost Warrior achievements.
Collect all secrets.
Win 50 rounds playing online. (Multiplayer)
Kill 2000 enemies. (Multiplayer)
Kill 500 people using sniper rifle. (Multiplayer)
Kill 250 people using sniper rifle. (Multiplayer)
Kill 250 people using pistol. (Multiplayer)
Kill 10 birds.
Complete Act 4.
Finish the game on Normal difficulty.
Finish the game on Hard difficulty.
Finish the game on Easy difficulty.
Kill 10 enemies with throwing knives.
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 2 enemy with one grenade.
Deliver 100 headshots.
Kill 15 enemy using concentration mode.
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.