Full list of all 80 XCOM 2 achievements worth 1,520 gamerscore. It takes around 150-200 hours to unlock all of the achievements in the base game on Xbox One.
The base game contains 50 achievements worth 1,000 Gamerscore, and there are 3 DLC packs containing 30 achievements worth 520 Gamerscore.
Sold goods worth 1000 supplies to the Black Market
Killed a Berserker in melee combat
Gotten all of the continent bonuses available in a single campaign
Built a radio relay on every continent
Caused an enemy to fall to its death
Overthrown the aliens at any difficulty level
Killed 3 enemies in a single turn, with a single soldier, without explosives
Created the Commander's Avatar
Completed the Avatar Autopsy
Built a facility in every Avenger slot
Killed 500 aliens
Killed an enemy with a hacked turret
Completely upgraded a beam weapon with superior grade weapon upgrades
Killed an Avatar
Recovered the Psi Gate
Hacked a Sectopod
Recovered the Forge Item
Killed a Sectopod on the same turn you encountered it (in Single Player)
Built the Shadow Chamber
Upgraded a facility
Sabotaged an alien facility
Applied a PCS upgrade to a soldier
Caused an enemy to die in a vehicle explosion
Built Resistance Comms
Upgraded a weapon
Built an experimental item in the Proving Grounds
Recovered the Blacksite Data
Killed a Sectoid who was mind controlling a squadmate
Recovered a Codex Brain
Killed a Viper who was strangling a squadmate
Skulljacked an ADVENT Officer
Beat a Retaliation mission with 3 or less civilian deaths
Made contact with a region
Completed a Rumor
Earned a second tier hack reward
Completed a successful ambush
Completed the tactical tutorial
Overthrow the aliens on Commander difficulty
Overthrow the aliens on Legend difficulty
Evacuate a soldier whose bleed-out timer is still running
Beat the game on Commander+ difficulty by July 1st
Beat the final mission using only conventional gear
Beat the game on Commander+ difficulty without buying a Squad Size upgrade
Beat the game on Commander+ without losing a soldier
Play in a multiplayer match
Beat a mission on Commander+ with a squad of soldiers only of the same class (but not Rookie)
Kill an enemy with every heavy weapon in the game (doesn't have to be in the same game)
Beat a mission in June or later using only Rookies
Skulljack each different type of ADVENT soldier (does not have to be in same game)
Beat the game on Commander+ difficulty in Ironman mode
Killed an alien ruler the first time you encountered it
Killed the Berserker Ruler
Killed all three alien rulers in a single game
Killed the Archon Ruler
Purchased all of the final tier hunter weapons
Killed the Viper Ruler
Investigated the Abandoned Research Facility
Use all ruler armor abilities in a single mission
Use a ruler armor ability against an alien ruler
Kill an alien ruler while it attempts to escape
Defeated an Avatar with a SPARK unit
Promoted a SPARK unit to Champion rank
Hit three shots on a single turn with a SPARK unit after using its Overdrive ability
Completed a mission with three or more SPARK units in the squad
Outfited a SPARK unit with the highest tier weaponry and armor
Built a SPARK unit
Beat the Lost Towers mission
Defeated a robotic enemy with a SPARK unit
Killed an enemy primed Derelict MEC before it can self-destruct
A SPARK unit survives a mission it started with less than half health
Got four kills from Shadow mode with a Reaper in a single mission
Raised XCOM's influence with all three factions to High in a single game
Formed a level 3 bond between two soldiers
Permanently defeated one of the Chosen
Rescued a soldier who was captured by the Chosen
Completed the Lost and Abandoned mission
Get 15 Headshots against Lost in a single turn
Raise a Templar to maximum Focus level, spend it all, and reach the max again in a single mission
Perform three offensive actions against the same target with a Skirmisher in a single turn
Complete a mission with all Tired soldiers and no casualties