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