Here is the full list of all 24 Sniper: Ghost Warrior achievements.
Kill 2000 enemies. (Multiplayer)
Kill 250 people using pistol. (Multiplayer)
Kill 250 people using sniper rifle. (Multiplayer)
Kill 500 people using sniper rifle. (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.
Shoot 5 cable lines using sniper rifles.
Complete Act 2.
Kill a total of 30 enemies with Browning gun.
Kill 2 enemy with one grenade.
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.
Kill 2 enemy with one shot.
Deliver 50 headshots.
Shoot an enemy through a wall.
Kill 10 birds.
Kill 15 enemy using concentration mode.