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.
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.
Defeat Dragonslayer Armour.
Reinforce any weapon to the highest level.
Defeat Dancer of the Boreal Valley.
Defeat Yhorm the Giant, Lord of Cinder.
Defeat Aldrich, Devourer of Gods, Lord of Cinder.
Discover Rosaria's Fingers covenant.
Defeat Old Demon King.
Defeat Pontiff Sulyvahn.
Defeat the Deacons of the Deep.
Become a Host of Embers for the first time.
Light a bonfire flame for the first time.
Complete all achievements.
Reach "The End of Fire" ending.
Reach "The Usurpation of Fire" ending.
Defeat the Abyss Watchers, Lords of Cinder.
Perform all forms of infusion.
Acquire all sorceries.
Acquire all pyromancies.
Acquire all miracles.
Acquire all rings.
Learn all gestures.
Reinforce a bonfire to the highest level.
Reinforce the Estus Flask to the highest level.
Discover Warrior of Sunlight covenant.
Discover Way of Blue covenant.
Discover Blue Sentinels covenant.
Discover Blade of the Darkmoon covenant.
Discover Mound-makers covenant.
Discover Watchdogs of Farron covenant.
Discover Aldrich Faithful covenant.
Defeat Iudex Gundyr.
Defeat Vordt of the Boreal Valley.
Defeat the Curse-rotted Greatwood.
Defeat Crystal Sage.
Defeat High Lord Wolnir.