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.
Acquire all miracles.
Acquire all sorceries.
Reach "To Link the First Flame" ending.
Learn all gestures.
Reach "The Usurpation of Fire" ending.
Perform all forms of infusion.
Defeat Nameless King.
Discover Mound-makers covenant.
Reach "The End of Fire" ending.
Defeat Ancient Wyvern.
Reinforce the Estus Flask to the highest level.
Reach Archdragon Peak.
Defeat Champion Gundyr.
Reinforce a bonfire to the highest level.
Discover Blade of the Darkmoon covenant.
Reach the Untended Graves.
Defeat Oceiros, the Consumed King.
Defeat Lothric, Younger Prince, Lord of Cinder.
Defeat Dragonslayer Armour.
Reinforce any weapon to the highest level.
Defeat Dancer of the Boreal Valley.
Defeat Yhorm the Giant, Lord of Cinder.
Discover Aldrich Faithful covenant.
Defeat Aldrich, Devourer of Gods, Lord of Cinder.
Defeat Pontiff Sulyvahn.
Defeat Old Demon King.
Discover Rosaria's Fingers covenant.
Defeat High Lord Wolnir.
Defeat the Deacons of the Deep.
Defeat the Abyss Watchers, Lords of Cinder.
Discover Watchdogs of Farron covenant.
Discover Warrior of Sunlight covenant.
Defeat Crystal Sage.
Defeat the Curse-rotted Greatwood.
Discover Way of Blue covenant.
Discover Blue Sentinels 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.
Complete all achievements.
Acquire all pyromancies.
Acquire all rings.