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