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