Full list of all 69 Halo: Reach achievements worth 1,700 gamerscore. It takes around 40-50 hours to unlock all of the achievements in the base game on Xbox 360.
The base game contains 49 achievements worth 1,000 Gamerscore, and there are 5 DLC packs containing 20 achievements worth 700 Gamerscore.
Complete each Campaign Mission on Legendary - alone.
Complete the Campaign on Legendary difficulty.
Purchase any item from the Armory.
Use a Health Pack to recover life after taking body damage.
Kill 10 Enemies in a Firefight or Campaign session with the M6G pistol.
Clear the 2nd mission without setting foot in a drivable vehicle.
Kill 7 Moa during the 2nd mission of the Campaign.
Kill 10 enemies in a Firefight or Campaign session with the DMR.
Complete the 2nd mission on Normal or harder.
Kill 2 vehicles at once with the Target Locator during the 3rd mission.
Trade weapons with an AI ally in Campaign.
Kill 10 enemies in Firefight or Campaign with a supercombine explosion.
Complete the 3rd mission on Normal or harder.
Perform an Assassination on an enemy.
Complete the 4th mission on Normal or harder.
Kill the Elite Zealot before he can escape during the 5th mission.
Complete the 5th mission on Normal or harder.
Destroy the Corvette's engines & escort in under 3 minutes in the 6th mission on Heroic or harder.
Complete the 6th mission on Normal or harder.
Earn a Triple Kill while Jetpacking in Campaign, Firefight or Matchmaking.
Complete the 7th mission on Normal or harder.
Reach the rank of Corporal in the UNSC.
Kill 3 of the anti-aircraft batteries during the 8th mission.
Complete the 8th mission on Normal or harder.
Finish the 9th mission on Legendary with the Scorpion intact.
Hijack a Banshee during the Reach Campaign.
Complete the 9th mission on Normal or harder.
Perform an Assassination against an Elite to survive a fall that would've been fatal.
Complete the 10th mission on Normal or harder.
Complete the Campaign on Heroic difficulty.
Complete the Campaign on Normal difficulty.
Earn a Killing Spree in multiplayer Matchmaking.
Let a teammate spawn on you 5 times in an Invasion Matchmaking game.
Win a game of Invasion in the 1st phase.
Earn a First Strike Medal in a Matchmaking game.
As an Elite, kill 5 Spartan players in Matchmaking.
Score 15,000 points in Score Attack Firefight Matchmaking.
Earn a Killionaire medal in Firefight.
Complete a Firefight set on Legendary without dying.
Score 50,000 points in Firefight on any map.
Score 200,000 points in Firefight on any map.
Score 1,000,000 points in Firefight on any map.
Using the File Browser upload a file to your File Share.
Complete a Weekly Challenge.
Recommend a file to someone.
Complete all of the Daily Challenges in a given day.
Reach the rank of Captain in the UNSC.
Advance any Commendation to its Silver state.
Purchase an item from the Armory that requires the rank of Lt. Colonel.
Noble 1: Earn a Double Kill from the Grave in multiplayer Matchmaking.
Noble 1: Earn a Double Kill with the shotgun in multiplayer Matchmaking.
Noble 1: Kill a player at long range with the DMR in a matchmade Slayer game.
Noble 1: Collect all of the flags in a matchmade Stockpile game.
Noble 1: Destroy a vehicle using Armor Lock in a matchmade game.
Noble 1: Earn a kill in a matchmade Rocket Race game.
Noble 1: Blow up the research facility in a matchmade Invasion game on Breakpoint.
Defiant: Successfully return two flags in a matchmade CTF game.
Defiant: Kill 3 players with the Oddball in a matchmade Oddball game.
Defiant: Capture two flags from an enemy capture zone in a matchmade Stockpile game.
Defiant: Prevent the attacking team from touching the flag in a matchmade 1-Flag CTF game.
Defiant: Assassinate a player that just exited Armor-Lock in a matchmade game.
Defiant: Be the last surviving uninfected player in a matchmade Infection game.
Anniversary: Get 3 headshot kills in a row in a matchmade game.
Anniversary: Infect 3 players in a single round in a matchmade Infection game.
Anniversary: Stick and kill the flag carrier with a Plasma Grenade in a matchmade game.
Anniversary: Perform a Beat Down on an enemy player while using the Jetpack during a matchmade game.
Anniversary: Run over 5 people with a vehicle in a matchmade game.
Anniversary: Capture 10 skulls at once in a matchmade Headhunter game.
Anniversary: Kill an enemy with their own Plasma Grenade that is stuck to you in a matchmade game.