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