Here is the full list of all 43 DARK SOULS III achievements. It takes around 80-100 hours to unlock all of the achievements on Windows.
Complete all achievements.
Reach "The End of Fire" ending.
Acquire all pyromancies.
Acquire all rings.
Acquire all sorceries.
Learn all gestures.
Acquire all miracles.
Reach "The Usurpation of Fire" ending.
Discover Mound-makers covenant.
Perform all forms of infusion.
Discover Blade of the Darkmoon covenant.
Discover Watchdogs of Farron covenant.
Discover Aldrich Faithful covenant.
Reinforce a bonfire to the highest level.
Reinforce the Estus Flask to the highest level.
Defeat Nameless King.
Defeat Ancient Wyvern.
Reach Archdragon Peak.
Defeat Champion Gundyr.
Reach the Untended Graves.
Defeat Oceiros, the Consumed King.
Reach "To Link the First Flame" ending.
Defeat Lothric, Younger Prince, Lord of Cinder.
Reinforce any weapon to the highest level.
Defeat Dragonslayer Armour.
Defeat Dancer of the Boreal Valley.
Discover Rosaria's Fingers covenant.
Defeat Yhorm the Giant, Lord of Cinder.
Defeat Aldrich, Devourer of Gods, Lord of Cinder.
Defeat Pontiff Sulyvahn.
Defeat Old Demon King.
Defeat the Deacons of the Deep.
Defeat Crystal Sage.
Defeat High Lord Wolnir.
Defeat the Abyss Watchers, Lords of Cinder.
Discover Warrior of Sunlight covenant.
Discover Blue Sentinels covenant.
Defeat the Curse-rotted Greatwood.
Discover Way of Blue covenant.
Defeat Vordt of the Boreal Valley.
Become a Host of Embers for the first time.
Defeat Iudex Gundyr.
Light a bonfire flame for the first time.