Here is the full list of all 51 Red Dead Redemption 2 achievements. It takes around 200 hours to unlock all of the achievements on Windows.
Attain 100% completion.
Find the graves of each of your fallen companions.
Red Dead Online: Reach Rank 50.
Red Dead Online: Take part in a Series.
Red Dead Online: Achieve MVP 3 times (in a round with at least 4 players).
Red Dead Online: Complete a Free Roam mission as part of a Posse with at least 2 members.
Red Dead Online: Concurrently own 5 horses.
Red Dead Online: Form a Persistent Posse.
Red Dead Online: Sell 20 items to the Butcher.
Red Dead Online: Purchase 5 camp improvements.
Red Dead Online: Craft 25 pieces of ammunition.
Red Dead Online: Craft 20 items (excluding ammo).
Red Dead Online: Accept 10 Free Roam missions from characters around the world.
Red Dead Online: Play 5 Free Roam Events.
Red Dead Online: Successfully counter a rival Posse's Free Roam mission.
Skin every species of animal in Story Mode.
Complete one of the Collectable strands.
Earn 70 Gold Medals in Story missions.
Study every animal across all states in Story Mode.
Craft 30 unique items in Story Mode.
Find a permanent home for the squirrel statue.
Survive 18 bear attacks and kill the bear each time in Story Mode.
Discover the fate of Marko Dragic.
Red Dead Online: Achieve 5 gold belt buckles from awards.
Red Dead Online: Pick 25 Herbs.
Red Dead Online: Reach Rank 10.
Complete the Epilogue.
Complete 'A New Jerusalem'.
Complete 'Red Dead Redemption'.
Complete all optional Honor story missions.
Complete 'Goodbye, Dear Friend'.
Catch a fish weighing at least 16 lbs (7.3 kg).
Complete Chapter 5.
Recover the stash from 4 homesteads.
Complete 10 Stranger mission strands.
Reach maximum or minimum Honor level.
Play all mini games.
Complete Chapter 4.
Survive 3 days holding a bounty of $250 in all states.
Spend $5000 across all shops.
Complete a Companion Activity in each camp.
Complete Chapter 3.
Complete Chapter 2.
Upgrade each available component for a single sidearm or longarm weapon.
Reach max bonding level with a horse.
Deliver 5 camp companion item requests.
Rob or loot $250.
Donate $250 to the gang tithing box.
Red Dead Online: Complete the Intro.
Complete Chapter 1.
Complete 'Enter, Pursued by a Memory'.