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