Here is the full list of all 75 Halo Wars: Definitive Edition achievements.
Complete the Campaign on Heroic Difficulty.
Complete the Campaign on Legendary Difficulty.
Finish all missions under Par Time on Heroic difficulty.
Play Halo Wars for at least 24 Total hours.
Finish five missions under Par Time on Heroic difficulty.
Win 30 Skirmish or Multiplayer Matches
Win a game on every Skirmish Map.
Unlock All Timeline Events.
Get a Gold Medal on every Campaign Mission.
Collect all Skulls.
Completed Mission 15 on any difficulty.
Obtain a lifetime campaign Score over 1,000,000.
Mission 15: Open the Doors in order.
Completed Mission 14 on any difficulty.
Mission 14: Don't claim an extra base.
Disrupt 5 active Leader Powers in a single game on Blood River.
Kill 20 enemy squads with a continuous Covenant Leader Power on Memorial Basin.
Finish one mission under Par Time on Heroic difficulty.
Win 20 Skirmish or Multiplayer Matches
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.
Score the winning point in a game of Keepaway against Legendary AI's.
Win a Public game.
Win and have the highest score in a Public Game.
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.
Use one of the 6 Major Leader Powers to destroy an enemy's last unit.
Mission 7: Do not destroy any Power Node.
Collect 8 Skulls.
Win a Skirmish Game with Dual Scarabs.
Win 10 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.
Win a 3v3 Skirmish game with 2 AI Allies.
Win a Skirmish Game with every Leader.
Get 20,000 points in any Skirmish Game.
Win a game in every Skirmish Game Mode.
Unlock 20 Timeline Events.
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.
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.
Improve your Score in any Campaign Mission.
Collect your first Skull.
Mission 2: Destroy every Methane Tank.
Completed Mission 5 on any difficulty.
Completed Mission 4 on any difficulty.
Mission 4: Save Adam.
Unlock a Timeline Event.
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.
Complete any Campaign Mission in Co-op Mode.
Completed Mission 1 on any difficulty.
Get a Gold Medal with all Debuff Skulls Active.
Mission 1: Ram and kill 50 Grunts with Warthogs.
100% Completion.
Win 40 Skirmish or Multiplayer Matches.
Win 50 Skirmish or Multiplayer Matches.
Win 100 Skirmish or Multiplayer Matches.
Win 75 Skirmish or Multiplayer Matches.