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
Killed an Avatar
Caused an enemy to fall to its death
Recovered the Forge Item
Built the Shadow Chamber
Hacked a Sectopod
Beat a Retaliation mission with 3 or less civilian deaths
Upgraded a facility
Sold goods worth 1000 supplies to the Black Market
Killed an enemy with a hacked turret
Killed 500 aliens
Recovered a Codex Brain
Skulljacked an ADVENT Officer
Killed a Sectopod on the same turn you encountered it (in Single Player)
Applied a PCS upgrade to a soldier
Recovered the Blacksite Data
Won a mission in June or later using only Rookies
Built Resistance Comms
Built an experimental item in the Proving Grounds
Caused an enemy to die in a vehicle explosion
Sabotaged an alien facility
Evacuated a soldier whose bleed-out timer was still running
Killed a Berserker in melee combat
Made contact with a region
Played in a multiplayer match
Killed a Sectoid who was mind controlling a squadmate
Killed 3 enemies in a single turn, with a single soldier, without explosives
Killed a Viper who was strangling a squadmate
Earned a second tier hack reward
Upgraded a weapon
Completed a Rumor
Completed a successful ambush
Completed the tactical tutorial
Overthrow the aliens on Commander difficulty
Overthrow the aliens on Legend difficulty
Recover the Psi Gate
Complete the Avatar Autopsy
Completely upgrade a beam weapon with superior grade weapon upgrades
Build a facility in every Avenger slot
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
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)
Build a radio relay on every continent
Get all of the continent bonuses available in a single campaign
Skulljack each different type of ADVENT soldier (does not have to be in same game)
Create the Commander's Avatar
Beat the game on Commander+ difficulty in Ironman mode
Killed an alien ruler while it attempted to escape
Killed the Berserker Ruler
Killed the Viper Ruler
Investigated the Abandoned Research Facility
Kill the Archon Ruler
Kill all three alien rulers in a single game
Purchase all of the final tier hunter weapons
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
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
Promote a SPARK unit to Champion rank
Complete a mission with three or more SPARK units in the squad
Defeat an Avatar with a SPARK unit
A SPARK unit survives a mission it started with less than half health
Hit three shots on a single turn with a SPARK unit after using its Overdrive ability
Got four kills from Shadow mode with a Reaper in a single mission
Rescued a soldier who was captured by the Chosen
Completed the Lost and Abandoned mission
Permanently defeat one of the Chosen
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
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