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