Here is the full list of all 75 Halo Wars: Definitive Edition achievements worth 1,500 gamerscore.
Completed the Campaign on Legendary Difficulty.
Disrupted 5 active Leader Powers in a single game on Blood River.
Finished with 5000 net resources tributed to your teammates on Memorial Basin except in Deathmatch.
Hot dropped 50 squads to your Covenant Leader in a single game on Barrens.
Mission 14: Didn't claim an extra base.
100% Completion.
Mission 10: Distrupted all Tractor Beams.
Won a 3v3 Skirmish game with 2 AI Allies.
Got a Gold Medal on every Campaign Mission.
Mission 7: Did not destroy any Power Node.
Mission 4: Saved Adam.
Mission 3: Killed at least 5 Covenant Units with the Bridge.
Got a Gold Medal with all Debuff Skulls Active.
Mission 12: Repaired the Power Core in less than 4 minutes.
Completed the Campaign on Heroic Difficulty.
Finished all missions under Par Time on Heroic difficulty.
Played Halo Wars for at least 24 Total hours.
Unlocked All Timeline Events.
Collected all Skulls.
Mission 8: Used Elephants to train 100 infantry.
Completed Mission 15 on any difficulty.
Mission 15: Opened the Doors in order.
Obtained a lifetime campaign Score over 1,000,000.
Won a Heroic Skirmish Game against the AI in under 10 minutes.
Got 20,000 points in any Skirmish Game.
Finished five missions under Par Time on Heroic difficulty.
Finished one mission under Par Time on Heroic difficulty.
Won 100 Skirmish or Multiplayer Matches.
Won 75 Skirmish or Multiplayer Matches.
Scored the winning point in a game of Keepaway against Legendary AI's.
Won 50 Skirmish or Multiplayer Matches.
Won 40 Skirmish or Multiplayer Matches.
Completed Mission 14 on any difficulty.
Got a Scarab during a Reinforcement game.
Won a game on every Skirmish Map.
Won 30 Skirmish or Multiplayer Matches
Completed Mission 9 on any difficulty.
Mission 9: Every Colony put in Hibernation Mode at the same time.
Completed Mission 8 on any difficulty.
Completed Mission 7 on any difficulty.
Collected 8 Skulls.
Won 20 Skirmish or Multiplayer Matches
Won a game in every Skirmish Game Mode.
Won a Skirmish Game with every Leader.
Unlock 20 Timeline Events.
Won 10 Skirmish or Multiplayer Matches
Won and never trailed in a Tug of War game.
Completed Mission 13 on any difficulty.
Mission 13: Destroyed 25 units with the Scarab.
Completed Mission 12 on any difficulty.
Completed Mission 11 on any difficulty.
Mission 11: Saved all the Airlocks.
Won a Public game.
Won and had the highest score in a Public Game.
Mission 5: Jacked 6 Covenant Vehicles.
Completed Mission 6 on any difficulty.
Mission 6: Successfully protected every Rhino.
Completed Mission 5 on any difficulty.
Completed Mission 4 on any difficulty.
Completed Mission 3 on any difficulty.
Gained at Least 15 population from a single wave in a Reinforcement game.
Mission 2: Destroyed every Methane Tank.
Got a winning High Score with 10 or less Squads against the Heroic AI.
Killed 20 enemy squads with a continuous Covenant Leader Power on Memorial Basin.
Won a Skirmish Game with Dual Scarabs.
Used one of the 6 Major Leader Powers to destroy an enemy's last unit.
Completed any Campaign Mission in Co-op Mode.
Completed Mission 10 on any difficulty.
Improved your Score in any Campaign Mission.
Completed Mission 2 on any difficulty.
Got a Gold Medal on any mission.
Completed Mission 1 on any difficulty.
Mission 1: Rammed and killed 50 Grunts with Warthogs.
Collected your first Skull.
Unlocked a Timeline Event.