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