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