I have finished most of the Horus heresy series, and thinking back, I wish I knew then what I know now in what order to read it. I personally read it in release order and I find it pretty sloppy and all over the place. While it is generally in chronological order, I didn't like how character arcs are interrupted with other stories and how long it takes for the story to return to said characters, because my memory is so bad. So with my proposed reading order, I decided to focus on characters and events. the highlighted names are the main books, while the unhighlighted names are tie-in short stories. In the end, this proposed reading order is by no means perfect and still probably is an unfinished mess and has much to improve and add, so don't be afraid to make suggestions. Enjoy!
- Horus Rising - Dan Abnett
- False Gods - Graham McNeill
- Galaxy in Flames - Ben Counter
- Fulgrim - Graham McNeill
- Legion - Dan Abnett
- Tales of Heresy: Wolf at the Door - Mike Lee
- Tales of Heresy: Blood Games - Dan Abnett
- War Without End: Howl of the Hearthworld - Aaron Dembski-Bowden
- Prospero Burns - Dan Abnett
- The Burden of Loyalty: The Thirteenth Wolf - Gav Thorpe
- The First Heretic - Aaron Dembski-Bowden
- Eye of Terra: Aurelian - Aaron Dembski-Bowden
- Battle for the Abyss - Ben Counter
- Know No Fear - Dan Abnett
- Mark of Calth
- The Burden of Loyalty: Perpetual - Dan Abnett
- Legacies of Betrayal: Honour to the Dead - Gav Thorpe
- The Honoured - Rob Sanders
- The Unburdened - David Annandale
- Legacies of Betrayal: Censure - Nick Kyme
- Heralds of the Siege: The Ember Wolves - Rob Sanders
- Tales of Heresy: After Desh'ea - Matthew Farrer
- War Without End: Lord of the Red Sands - Aaron Dembski-Bowden
- Legacies of Betrayal: Butcher's Nails - Aaron Dembski-Bowden
- Betrayer - Aaron Dembski-Bowden
- Legacies of Betrayal: Khârn: The Eightfold Path - Anthony Reynolds
- Legacies of Betrayal: Heart of the Conqueror - Aaron Dembski-Bowden
- Heralds of the Siege: Children of Sicarus - Anthony Reynolds
- Age of Darkness: Rules of Engagement - Graham McNeill
- Shadows of Treachery: Raven's Flight - Gav Thorpe
- Age of Darkness: The Face of Treachery - Gav Thorpe
- Deliverance Lost - Gav Thorpe
- Heralds of the Siege: The Grey Raven - Gav Thorpe
- Age of Darkness: The Iron Within - Rob Sanders
- Eye of Terra: Ironfire - Rob Sanders
- The Primarchs: The Reflection Crack'd - Graham McNeill
- Legacies of Betrayal: Kryptos - Graham McNeill
- Angel Exterminatus - Graham McNeill
- Shattered Legions: The Seventh Serpent - Graham McNeill
- The Outcast Dead - Graham McNeill
- The Silent War: Wolf Hunt - Graham McNeill
- A Thousand Sons - Graham McNeill
- Legacies of Betrayal: Thief of Revelations - Graham McNeill
- Legacies of Betrayal: Lucius: The Eternal Blademaster - Graham McNeill
- The Crimson King - Graham McNeill
- The Flight of the Eisenstein - James Swallow
- Shadows of Treachery: The Crimson Fist - John French
- Nemesis - James Swallow
- War Without End: Gunsight - James Swallow
- Garro - James Swallow
- Tales of Heresy: Scions of the Storm - Anthony Reynolds
- The Silent War: The Purge - Anthony Reynolds
- Tales of Heresy: The Voice - James Swallow
- The Silent War: Ghosts Speak Not - James Swallow
- The Silent War: Patience - James Swallow
- Fear to Tread - James Swallow
- The Primarchs: The Serpent Beneath - Rob Sanders
- Legacies of Betrayal: Brotherhood of the Storm - Chris Wraight
- Scars - Chris Wraight
- Eye of Terra: Brotherhood of the Moon - Chris Wraight
- Legacies of Betrayal: Wolf's Claw - Chris Wraight
- The Burden of Loyalty: Wolf King - Chris Wraight
- War Without End: Daemonology - Chris Wraight
- War Without End: The Devine Adoratrice - Graham McNeill
- Age of Darkness: Little Horus - Dan Abnett
- Vengeful Spirit - Graham McNeill
- War Without End: Wolf Mother - Graham McNeill
- War Without End: Imperfect - Nick Kyme
- War Without End: Chirurgeon - Nick Kyme
- Legacies of Betrayal: Warmaster - John French
- Age of Darkness: Rebirth - Chris Wraight
- War Without End: Allegiance - Chris Wraight
- The Path of Heaven - Chris Wraight
- Heralds of the Siege: The Last Son of Prospero - Chris Wraight
- War Without End: All That Remains - James Swallow
- War Without End: Black Oculus - John French
- Tallarn - John French
- Eye of Terra: The Eagle's Talon - John French
- Eye of Terra: Iron Corpses - John French
- Heralds of the Siege: Dark Compliance - John French
- The Buried Dagger - James Swallow (to me this book fits here and also at the end, just after Titendeath)
- Born of Flame: Promethean Sun - Nick Kyme
- Born of Flame: Scorched Earth - Nick Kyme
- Vulkan lives - Nick Kyme
- Descent of Angels - Mitchel Scanlon
- Fallen Angels - Mike Lee
- Age of Darkness: Savage Weapons - Aaron Dembski-Bowden
- The Primarchs: The Lion - Gav Thorpe
- Shadows of Treachery: Prince of Crows - Aaron Dembski-Bowden
- The Unremembered Empire - Dan Abnett
- War Without End: The Laurel of Defiance - Guy Haley
- War Without End: Virtues of the Sons - Andy Smillie
- Eye of Terra: Sins of the Father - Andy Smillie
- Eye of Terra: Herald of Sanguinius - Andy Smillie
- War Without End: A Safe and Shadowed Place - Guy Haley
- Eye of Terra: The Long Night - Aaron Dembski-Bowden
- The Burden of Loyalty: The Heart of the Pharos - L. J. Goulding
- Pharos - Guy Haley
- Heralds of the Siege: The Painted Count - Guy Haley
- Legacies of Betrayal: Cypher: Guardian of Order - Gav Thorpe
- Eye of Terra: Master of the First - Gav Thorpe
- War Without End: By the Lion's Command - Gav Thorpe
- Angels of Caliban - Gav Thorpe
- Heralds of the Siege: Exocytosis - James Swallow
- Eye of Terra: Red-Marked - Nick Kyme
- Eye of Terra: Stratagem - Nick Kyme
- Deathfire - Nick Kyme
- Shadows of Treachery: The Kaban Project - Graham McNeill
- Mechanicum - Graham McNeill
- The Burden of Loyalty: Cybernetica - Rob Sanders
- Heralds of the Siege: Myriad - Rob Sanders
- Eye of Terra: Vorax - Matthew Farrer
- The Burden of Loyalty: The Binary Succession - David Annandale
- Tales of Heresy: The Last Church - Graham McNeill
- The Silent War: The Sigillite - Chris Wraight
- The Burden of Loyalty: Into Exile - Aaron Dembski-Bowden
- Master of Mankind - Aaron Dembski-Bowden
- Heralds of the Siege: Magisterium - Chris Wraight
- The Burden of Loyalty: Ordo Sinister - John French
- The Primarchs: Feat of Iron - Nick Kyme
- Shattered Legions: Meduson - Dan Abnett
- Legacies of Betrayal: Riven - John French
- Born of Flame: Artefacts - Nick Kyme
- Born of Flame: Sons of the Forge - Nick Kyme
- Old Earth - Nick Kyme
- Shadows of Treachery: The Dark King - Graham McNeill
- Shadows of Treachery: The Lightning Tower - Dan Abnett
- Praetorian of Dorn - John French
- Legacies of Betrayal: Veritas Ferrum - David Annandale
- The Damnation of Pythos - David Annandale
- Ruinstorm - David Annandale
- Wolfsbane - Guy Haley
- Heralds of the Siege: Duty Waits - Guy Haley
- Heralds of the Siege: The Soul, Severed - Chris Wraight
- Slaves to Darkness - John French
- Corax: Weregeld - Gav Thorpe
- Legacies of Betrayal: The Divine Word - Gav Thorpe
- Heralds of the Siege: Valerius - Gav Thorpe
- Titendeath - Guy Haley
- Heralds of the Siege: Now Peals Midnight - John French
- Heralds of the Siege: The Board is Set - Nick Kyme