Timing is everything. In the Reaper War, it's literally the difference between life and death. If you mess up your Mass Effect 3 mission order, you’ll end up staring at a memorial wall full of names that didn't have to be there. I’ve played through this trilogy more times than I care to admit, and the biggest mistake people make is rushing. They see the "Priority" tag on a mission and think they need to do it immediately. That’s a trap. BioWare designed those labels to create a sense of urgency, but in reality, "Priority" usually means "this will lock out side quests and potentially kill your friends."
The galaxy is falling apart. Earth is under siege. Palaven is burning. It’s easy to feel like you should be sprinting toward the finish line, but Mass Effect 3 is a game of patience disguised as a race against time.
Why your Mass Effect 3 mission order actually matters
Let’s talk about the Grissom Academy mission. If you ignore that distress call for too long because you’re busy chasing the main plot, Jack and her students meet a fate much worse than death. They get turned into Cerberus phantoms. You’ll actually have to fight them later. It’s brutal. This isn't just about getting 100% completion; it’s about the narrative weight of your choices.
The game is structured into three distinct acts, separated by massive, world-altering events. Most side content—the stuff labeled "N7" or "Citadel"—has an expiration date. Usually, these missions need to be cleared before you hit the next "Priority" beat. If you don't, they disappear from your log, and you lose out on War Assets. War Assets are the invisible math that determines if Shepard lives or if the Earth becomes a pile of radioactive dust.
Honestly, the game doesn't do a great job of explaining this. It tells you the Reapers are coming, then gets mad at you for trying to stop them too quickly. You have to balance the Reaper threat with the micro-politics of the various alien races.
Act 1: The Pre-Tuchanka Hustle
After you leave Mars and get your bearings on the Citadel, the game opens up. This is where you need to be careful. Your first major goal is the krogan homeworld, but don't go there yet.
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Do everything else first.
- Priority: Palaven – You have to do this to get Garrus. It’s non-negotiable and doesn't lock anything out.
- Grissom Academy: Investigation – Do this IMMEDIATELY after Palaven. It’s one of the few missions with a literal timer. If you complete three other missions first, it’s gone.
- The Citadel Side Quests – Walk around. Listen to people. Use your map. There are dozens of tiny fetch quests that give you War Assets.
- Sur'Kesh – This is the start of the Genophage arc.
Once you finish Sur'Kesh, the game throws a bunch of Tuchanka-related missions at you. Here is where the Mass Effect 3 mission order gets tricky. You’ll see "Priority: Tuchanka," but you also see "Tuchanka: Bomb" and "Attican Traverse: Krogan Team."
Do the Krogan Team (Grunt’s mission) and the Bomb mission before you touch the Priority mission. If you cure the Genophage first, the Bomb mission might disappear, or the bomb might actually go off, costing you thousands of lives. It’s a mess.
The Mid-Game Slump and the Geth/Quarian Conflict
Once Tuchanka is settled, the game shifts focus to the Perseus Veil. This is Act 2. Again, the "Priority" label is your enemy. You’ll be tempted to rush through Rannoch to see how the war between the Geth and Quarians ends. Don't.
If you want to broker peace—which is the "golden" ending for that arc—you need to do the side missions. Specifically, you must complete "Rannoch: Admiral Koris" and "Rannoch: Geth Fighter Squadrons."
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Missing these doesn't just lose you some dialogue. It makes peace impossible. You’ll be forced to choose between the total extinction of the Quarians or the total destruction of the Geth. It’s one of the most heartbreaking moments in the series if you haven't done the legwork. Also, save Admiral Koris. I know he’s annoying, but he’s essential for the peace points calculation.
Handling the DLC: When to play Leviathan and Omega
Integration of DLC is where most players get confused. Since these weren't in the base game at launch, their placement in the Mass Effect 3 mission order feels a bit "tacked on." But they provide massive context.
Omega is best played whenever you feel like Shepard needs a break from the main stress. It doesn't have a huge impact on the ending, but it gives you some great power-ups. I usually do it right after the Citadel coup.
Leviathan is different. This is deep lore. It explains the origins of the Reapers. If you do it too early, it feels weirdly out of place. If you do it too late, you’re already in the endgame. The best way to play Leviathan is to treat it like a detective story spread across the whole game. Do one part after Tuchanka, one part after Rannoch, and the final part just before the point of no return.
Citadel DLC is the big one. This is the fan-service masterpiece. Whatever you do, do not play the party at the end of this DLC until right before the final assault on Cronos Station. You want every possible squadmate to be there. If you do it early, the room feels empty. It’s meant to be a "last hurrah," so treat it like one.
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The Point of No Return
Eventually, you’ll get the mission "Priority: Thessia." This is a turning point. After Thessia, the game starts to pull you toward the end. But the real "hard lock" is Priority: Cerberus Headquarters (Cronos Station).
Once you start the assault on Cronos Station, there is no going back. You can't visit the Citadel. You can't finish side quests. You can't scan planets for extra fuel or assets. This is the moment. Before you click that mission on the galaxy map, make sure your Galactic Readiness is as high as possible.
If you’re playing the Legendary Edition, the requirements for the "best" endings are higher because you don't have the multiplayer component to boost your scores. You need roughly 7,400 Total Military Strength before the Cerberus base to unlock everything. That sounds like a lot. It is. But if you followed a solid Mass Effect 3 mission order, you’ll hit it easily.
Common Mistakes to Avoid
- Ignoring the Academy: I mentioned it before, but seriously, do Grissom Academy.
- Rushing the Genophage: Tuchanka is huge. Take your time. Talk to Eve. Talk to Mordin.
- Forgetting the Scans: Probing planets for war assets is boring. I get it. But those tiny 25-point assets add up to the difference between Shepard breathing at the end or not.
- The Citadel Coup: After the Tuchanka arc, the Citadel changes. Many side quests there will fail if they aren't finished before the coup. Clean out your quest log before you finish the "Priority: Tuchanka" mission.
Actionable Steps for your Playthrough
To ensure the best outcome for your Shepard and the galaxy, follow this logic for your mission queue:
- Check the Citadel after every major mission. New NPCs appear, and old ones have new things to say. This is where most of your War Assets come from.
- Prioritize "Timed" missions. If a mission sounds like an emergency (like a bomb or a school under attack), it probably is. Do those before anything labeled "Priority."
- Clear the Rannoch side missions. You need the Geth and the Quarians to play nice. You can't do that if you ignore the Geth Fighter Squadrons mission.
- Save the Citadel DLC Party for last. Complete the Cerberus Headquarters mission only after you've had your party and said your goodbyes.
- Max out your Paragon or Renegade score. Many of the best outcomes in these missions require high charisma checks. If you flip-flop too much, you won't have the points to save everyone.
The war for the galaxy isn't won on the battlefield of London; it's won in the dozens of hours leading up to it by being in the right place at the right time. Manage your journal, respect the timers, and keep your squad alive.
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