Full list of all 42 Cult of the Lamb achievements worth 1,140 gamerscore. It takes around 20-25 hours to unlock all of the achievements in the base game.
The base game contains 37 achievements worth 1,000 Gamerscore, and there is 1 DLC pack containing 5 achievements worth 140 Gamerscore.
The first devotee to the Cult of the Lamb.
A deal that cannot be undone.
Let the Word be known.
Salvation awaits the fallen soul.
Defeat the first mini-boss.
Gain 5 Followers.
Gain 10 Followers.
Gain 20 Followers.
Defeat Leshy.
Defeat Heket.
Defeat Kallamar.
Defeat Shamura.
Defeat the One Who Waits.
Beat Leshy without taking damage.
Beat Heket without taking damage.
Beat Kallamar without taking damage.
Beat Shamura without taking damage.
Take confession.
Find all 5 locations.
Reignite the lighthouse.
Unlock all Follower Skins.
Unlock all tarot cards.
Catch 1 of every fish.
A new world awaits.
Sacrifice a Follower.
Sacrifice 10 Followers.
Have 666 gold coins.
Unlock all weapons.
Unlock all curses.
Fully Upgrade Cult.
Unlock a new fleece.
Unlock all fleeces.
Cook a Follower meat meal.
Unlock all doctrines.
Win a game of Knucklebones.
Defeat all opponents in Knucklebones.
No longer a servant, no less than a God.
Collect all Relics.
Get your Gold back from Midas.
Reunite Aym and Baal with Forneus.
Complete a row in Purgatory.
Indoctrinate all five Bishops into your Cult.