Here is the full list of all 75 Halo Wars: Definitive Edition achievements.
Complete the Campaign on Legendary Difficulty.
Get a Gold Medal on every Campaign Mission.
100% Completion.
Win 100 Skirmish or Multiplayer Matches.
Win a Public game.
Win and have the highest score in a Public Game.
Complete any Campaign Mission in Co-op Mode.
Win 75 Skirmish or Multiplayer Matches.
Win 50 Skirmish or Multiplayer Matches.
Win 40 Skirmish or Multiplayer Matches.
Win a game on every Skirmish Map.
Win 30 Skirmish or Multiplayer Matches
Unlock All Timeline Events.
Disrupt 5 active Leader Powers in a single game on Blood River.
Win 20 Skirmish or Multiplayer Matches
Kill 20 enemy squads with a continuous Covenant Leader Power on Memorial Basin.
Hot drop 50 squads to your Covenant Leader in a single game on Barrens.
Finish with 5000 net resources tributed to your teammates on Memorial Basin except in Deathmatch.
Get a Scarab during a Reinforcement game.
Gain at Least 15 population from a single wave in a Reinforcement game.
Win and never trail in a Tug of War game.
Get a winning High Score with 10 or less Squads against the Heroic AI.
Win a Skirmish Game with Dual Scarabs.
Win a 3v3 Skirmish game with 2 AI Allies.
Win 10 Skirmish or Multiplayer Matches
Get 20,000 points in any Skirmish Game.
Score the winning point in a game of Keepaway against Legendary AI's.
Win a Heroic Skirmish Game against the AI in under 10 minutes.
Win a Skirmish Game with every Leader.
Play Halo Wars for at least 24 Total hours.
Win a game in every Skirmish Game Mode.
Unlock 20 Timeline Events.
Get a Gold Medal with all Debuff Skulls Active.
Collect all Skulls.
Mission 12: Repair the Power Core in less than 4 minutes.
Mission 7: Do not destroy any Power Node.
Use one of the 6 Major Leader Powers to destroy an enemy's last unit.
Finish all missions under Par Time on Heroic difficulty.
Obtain a lifetime campaign Score over 1,000,000.
Complete the Campaign on Heroic Difficulty.
Completed Mission 15 on any difficulty.
Mission 15: Open the Doors in order.
Completed Mission 14 on any difficulty.
Mission 14: Don't claim an extra base.
Completed Mission 13 on any difficulty.
Mission 13: Destroy 25 units with the Scarab.
Improve your Score in any Campaign Mission.
Completed Mission 12 on any difficulty.
Completed Mission 11 on any difficulty.
Mission 11: Save all the Airlocks.
Finish five missions under Par Time on Heroic difficulty.
Completed Mission 10 on any difficulty.
Mission 10: Distrupt all Tractor Beams.
Completed Mission 9 on any difficulty.
Mission 9: Put every Colony in Hibernation Mode at the same time.
Completed Mission 8 on any difficulty.
Collect 8 Skulls.
Mission 8: Use Elephants to train 100 infantry.
Completed Mission 7 on any difficulty.
Completed Mission 6 on any difficulty.
Mission 6: Successfully protect every Rhino.
Mission 5: Jack 6 Covenant Vehicles.
Completed Mission 5 on any difficulty.
Completed Mission 4 on any difficulty.
Mission 4: Save Adam.
Completed Mission 3 on any difficulty.
Mission 3: Kill at least 5 Covenant Units with the Bridge.
Completed Mission 2 on any difficulty.
Mission 2: Destroy every Methane Tank.
Mission 1: Ram and kill 50 Grunts with Warthogs.
Get a Gold Medal on any mission.
Completed Mission 1 on any difficulty.
Finish one mission under Par Time on Heroic difficulty.
Collect your first Skull.
Unlock a Timeline Event.