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