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