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 Ancient Wyvern.
Reach "To Link the First Flame" ending.
Reach Archdragon Peak.
Defeat Champion Gundyr.
Reach the Untended Graves.
Defeat Oceiros, the Consumed King.
Discover Blade of the Darkmoon covenant.
Reach "The Usurpation of Fire" ending.
Reinforce any weapon to the highest level.
Defeat Lothric, Younger Prince, Lord of Cinder.
Defeat Dragonslayer Armour.
Defeat Dancer of the Boreal Valley.
Defeat Yhorm the Giant, Lord of Cinder.
Defeat Aldrich, Devourer of Gods, Lord of Cinder.
Discover Aldrich Faithful covenant.
Defeat Old Demon King.
Defeat High Lord Wolnir.
Defeat the Abyss Watchers, Lords of Cinder.
Defeat Pontiff Sulyvahn.
Discover Watchdogs of Farron covenant.
Discover Rosaria's Fingers covenant.
Defeat the Deacons of the Deep.
Defeat the Curse-rotted Greatwood.
Defeat Crystal Sage.
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.
Reach "The End of Fire" ending.
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 Mound-makers covenant.
Defeat Nameless King.