Here is the full list of all 75 Halo Wars: Definitive Edition achievements.
Kill 20 enemy squads with a continuous Covenant Leader Power on Memorial Basin.
Win a Public game.
Win and have the highest score in a Public Game.
Complete any Campaign Mission in Co-op Mode.
Win 50 Skirmish or Multiplayer Matches.
100% Completion.
Win a game on every Skirmish Map.
Unlock All Timeline Events.
Win 40 Skirmish or Multiplayer Matches.
Get 20,000 points in any Skirmish Game.
Hot drop 50 squads to your Covenant Leader in a single game on Barrens.
Get a Scarab during a Reinforcement game.
Gain at Least 15 population from a single wave in a Reinforcement game.
Win 30 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 20 Skirmish or Multiplayer Matches
Win a Skirmish Game with Dual Scarabs.
Get a winning High Score with 10 or less Squads against the Heroic AI.
Play Halo Wars for at least 24 Total hours.
Finish five missions under Par Time on Heroic difficulty.
Win 10 Skirmish or Multiplayer Matches
Finish with 5000 net resources tributed to your teammates on Memorial Basin except in Deathmatch.
Mission 1: Ram and kill 50 Grunts with Warthogs.
Get a Gold Medal with all Debuff Skulls Active.
Win a Heroic Skirmish Game against the AI in under 10 minutes.
Get a Gold Medal on every Campaign Mission.
Mission 6: Successfully protect every Rhino.
Collect all Skulls.
Unlock 20 Timeline Events.
Obtain a lifetime campaign Score over 1,000,000.
Completed Mission 15 on any difficulty.
Mission 15: Open the Doors in order.
Mission 14: Don't claim an extra base.
Completed Mission 14 on any difficulty.
Mission 10: Distrupt all Tractor Beams.
Completed Mission 13 on any difficulty.
Mission 13: Destroy 25 units with the Scarab.
Completed Mission 12 on any difficulty.
Mission 12: Repair the Power Core in less than 4 minutes.
Completed Mission 11 on any difficulty.
Mission 11: Save all the Airlocks.
Completed Mission 10 on any difficulty.
Collect 8 Skulls.
Completed Mission 9 on any difficulty.
Mission 9: Put every Colony in Hibernation Mode at the same time.
Mission 8: Use Elephants to train 100 infantry.
Completed Mission 8 on any difficulty.
Win a 3v3 Skirmish game with 2 AI Allies.
Completed Mission 7 on any difficulty.
Mission 7: Do not destroy any Power Node.
Use one of the 6 Major Leader Powers to destroy an enemy's last unit.
Finish one mission under Par Time on Heroic difficulty.
Mission 4: Save Adam.
Completed Mission 6 on any difficulty.
Completed Mission 5 on any difficulty.
Mission 5: Jack 6 Covenant Vehicles.
Collect your first Skull.
Completed Mission 4 on any difficulty.
Improve your Score in any Campaign Mission.
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.
Unlock a Timeline Event.
Get a Gold Medal on any mission.
Completed Mission 1 on any difficulty.
Complete the Campaign on Heroic Difficulty.
Complete the Campaign on Legendary Difficulty.
Finish all missions under Par Time on Heroic difficulty.
Score the winning point in a game of Keepaway against Legendary AI's.
Win 100 Skirmish or Multiplayer Matches.
Win 75 Skirmish or Multiplayer Matches.
Disrupt 5 active Leader Powers in a single game on Blood River.