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.
Overthrown the aliens at any difficulty level
Created the Commander's Avatar
Gotten all of the continent bonuses available in a single campaign
Built a radio relay on every continent
Built a facility in every Avenger slot
Completed the Avatar Autopsy
Recovered the Psi Gate
Killed an Avatar
Recovered the Forge Item
Killed 3 enemies in a single turn, with a single soldier, without explosives
Killed a Sectopod on the same turn you encountered it (in Single Player)
Caused an enemy to die in a vehicle explosion
Killed 500 aliens
Built Resistance Comms
Sabotaged an alien facility
Built the Shadow Chamber
Upgraded a facility
Beat a Retaliation mission with 3 or less civilian deaths
Applied a PCS upgrade to a soldier
Killed a Viper who was strangling a squadmate
Recovered the Blacksite Data
Killed a Sectoid who was mind controlling a squadmate
Completed a Rumor
Recovered a Codex Brain
Built an experimental item in the Proving Grounds
Skulljacked an ADVENT Officer
Upgraded a weapon
Made contact with a region
Completed a successful ambush
Completed the tactical tutorial
Overthrow the aliens on Commander difficulty
Overthrow the aliens on Legend difficulty
Sell goods worth 1000 supplies to the Black Market (Can span multiple games)
Hack a Sectopod
Evacuate a soldier whose bleed-out timer is still running
Completely upgrade a beam weapon with superior grade weapon upgrades
Kill a Berserker in melee combat
Kill an enemy with a hacked turret
Cause an enemy to fall to its death
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)
Earn a second tier hack reward
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 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
Kill an alien ruler the first time you encounter it
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
Outfited a SPARK unit with the highest tier weaponry and armor
Completed a mission with three or more SPARK units in the squad
Promoted a SPARK unit to Champion rank
A SPARK unit survived a mission it started with less than half health
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
Hit three shots on a single turn with a SPARK unit after using its Overdrive ability
Complete the Lost and Abandoned mission
Permanently defeat one of the Chosen
Get 15 Headshots against Lost in a single turn
Get four kills from Shadow mode with a Reaper in a single mission
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
Form a level 3 bond between two soldiers
Complete a mission with all Tired soldiers and no casualties
Raise XCOM's influence with all three factions to High in a single game
Rescue a soldier who was captured by the Chosen