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