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