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