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