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