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