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