Here is the full list of all 39 The Banner Saga achievements. It takes around 25-30 hours to unlock all of the achievements on Windows.
Complete the game on Hard difficulty.
Complete the game on Hard difficulty level without losing a single battle.
Defeat an enemy with a Backbiter.
Defeat an enemy with a Siege Archer.
Complete the game without ever getting low morale.
Whew...Egil made it the whole way!
Win a battle on Hard difficulty in the camp Training Tent using 6 rank 5 units.
Fight 40 battles in a single playthrough.
Complete the game without letting anyone in your caravan die to hunger.
Alette doesn't want to harm humans or varl...don't make her.
Complete the game on Normal difficulty.
Reach Boersgard in 120 days.
Get permission to destroy a varl landmark.
Acquire 5 rank 5 items.
Visit the godstone Stravhs.
Defeat an enemy with a Thrasher.
Defeat an enemy with a Bowmaster.
Defeat an enemy with a Skystriker.
Defeat an enemy with a Strongarm.
Defeat an enemy with a Shieldmaster.
Defeat an enemy with a Provoker.
Defeat an enemy with a Warmaster.
Defeat an enemy with a Warleader.
Defeat an enemy with a Hunter.
Defeat an enemy with a Spearmaster.
Defeat an enemy with an Eagle Eye.
Defeat an enemy with a Mender.
Visit the godstone Denglr.
Visit the godstone Hadrborg.
Visit the godstone Hridvaldyr.
Visit the godstone Marek.
Visit the godstone Radormyr.
Visit the godstone Bjorulf.
Visit the godstone Dundr.
Visit the godstone Ingrid.
Defeat an enemy with a Grudgewielder.
Defeat an enemy with a Warden.
Defeat an enemy with a Raidmaster.
Defeat an enemy with a Warhawk.