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