Full list of all 73 Halo 5: Guardians achievements worth 1,250 gamerscore. It takes around 40-50 hours to unlock all of the achievements in the base game.
The base game contains 65 achievements worth 1,000 Gamerscore, and there are 2 DLC packs containing 8 achievements worth 250 Gamerscore.
Found and claimed all Intel.
Found and claimed all Skulls.
Completed every Mission of the game by yourself on Legendary difficulty.
Completed every Mission of the game on Normal difficulty.
Completed every Mission of the game on Heroic difficulty.
Completed every Mission of the game on Legendary difficulty.
Completed Mission 15.
Completed Mission 14.
Completed Mission 13.
Finished the 13th mission without losing the Scorpion on Legendary difficulty.
Operated four different vehicles at once in Mission 13 on Heroic difficulty.
Completed Mission 12.
Killed a Grunt and smashed a grate with a Ground Pound in Battle of Sunaion.
Completed Mission 11.
Completed any Mission with 3+ Skulls active on Heroic difficulty.
Completed Enemy Lines without destroying a Kraken turret.
Escaped the doomed Kraken by jumping onto a Phaeton piloted by a Spartan.
Destroyed the Phantom at the Covenant camp in Reunion on Heroic difficulty.
Destroyed 10 walls or floors in Swords of Sanghelios.
Traversed the canyon without a Phaeton in Reunion on Heroic difficulty.
Completed Mission 10.
Completed Mission 9.
Completed Mission 8.
Spectated a game.
Qualified for a Competitive Skill Rating.
Completed Glassed without any players using Smart-Link.
Simultaneously assassinated two Elites in Blue Team co-op.
Completed 5 matchmade games of Breakout.
Completed Glassed without entering a vehicle.
Completed Mission 7.
Escaped the Hunters in the lab and fought them in the hangar in Blue Team.
Killed a Legendary Boss in Warzone.
Won a match on all three original Warzone maps.
Completed Mission 6.
Completed Mission 5.
Killed an enemy that's had its armor repaired in Unconfirmed.
Created and saved a Custom Game.
Completed 5 matchmade games of Slayer.
Completed 3 matchmade games of Warzone.
Called in a REQ that costs 5 Energy or more.
Opened a Gold REQ Pack.
Completed Mission 4.
Completed Mission 3.
Completed Mission 2.
Completed Mission 1.
Completed any co-op Mission on Heroic difficulty.
Found and claimed a Skull.
Commanded your team of Spartans in Osiris.
Found and claimed one piece of Intel.
Changed your Emblem in the Spartan Hub.
Changed your Service Tag in the Spartan Hub.
Changed your Spartan's gear in the Spartan Hub.
Complete 5 matchmade games of Strongholds.
Complete 5 matchmade games of Capture the Flag.
Finish Evacuation within 18:00 without dying on Heroic difficulty.
Help the Elite General charge the hill in Osiris on Heroic difficulty.
Team up in a vehicle to kill 30 enemies in Unconfirmed co-op.
Keep 6 miners alive at the elevator in Evacuation on Heroic difficulty.
Complete Swords of Sanghelios co-op with both Mantises on Heroic difficulty.
Knock two Hunters into the ocean during the Battle of Sunaion.
Complete The Breaking on Legendary difficulty without the entire fireteam dying.
Simultaneously kill two Wardens in The Breaking on Heroic difficulty.
Use a Ground Pound on an exterior power core in Guardians on Heroic difficulty.
Simultaneously destroy 2 cores in Guardians on Heroic difficulty.
Complete every co-op Mission on Heroic difficulty.
Complete a mission in Score Attack with at least 10,000 points.
Reach 50,000 points in Score Attack with a Skull multiplier of x2 or higher.
Complete a mission in Score Attack co-op, with all participants scoring at least 200,000 points.
Beat the par time of a mission in Score Attack.
Complete a mission in Score Attack with at least 500,000 points.
Successfully complete 5 Warzone Firefight matches.
Complete a Warzone Firefight match on 6 unique maps.
Earn a Mythic Boss Takedown in a Warzone Firefight match.