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