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