The project began in October 2013 when Marvel Television was reported to be preparing four drama series and a miniseries totaling 60 episodes for streaming and cable providers, before Netflix committed to the four interconnected shows leading up to The Defenders.

Marvel Comics editor-in-chief Joe Quesada explained that changing the Defenders lineup from the classic comics team (Doctor Strange, Hulk, Namor, and Silver Surfer) to Daredevil, Jessica Jones, Luke Cage, and Iron Fist felt natural since general audiences did not know the original team-up.

Showrunner Marco Ramirez said the choice to kill off Elektra Natchios at the end of Daredevil season 2 was made organically by that show's writers, and executive producer Jeph Loeb pushed to adapt her comic book resurrection storyline in The Defenders instead.

Showrunners deliberately avoided comparisons to The Avengers, citing The Dirty Dozen and Seven Samurai as bigger influences since they feature reluctant characters forced to work together, and chose not to give the team a shared headquarters or matching costumes.

Co-showrunner Doug Petrie left the project right as filming began in October 2016, with Loeb explaining that once the scripts were finished, Petrie pursued other opportunities while Ramirez continued as sole showrunner.

Before Sigourney Weaver was cast, producers had referred to the villain role for four months internally as 'a Sigourney Weaver type' before Jeph Loeb actually approached her about playing Alexandra.

Costume designer Stephanie Maslansky had to choose between working on The Defenders or the first season of The Punisher due to a scheduling conflict, and picked The Defenders so she could complete the culmination of her costume work across all the Netflix Marvel shows.

Filming took place under the working title 'Group Therapy' and ran from October 31, 2016 to March 19, 2017, overlapping partly with production on Jessica Jones season 2.

Director S. J. Clarkson used vintage Panavision lenses for her two episodes, but supply and workability issues led cinematographer Matthew J. Lloyd to switch to modern Arri Master Prime lenses for the rest of the series.

The miniseries used so much steadicam work that the production essentially had two A-camera steadicam operators working simultaneously.

The opening sword-fight sequence, shot in a wet tunnel, caused significant on-set issues for the crew due to water covering the set.

Composer John Paesano wove music by Johannes Brahms throughout the score, including a live performance of his First String Quartet by the real-life Aeolus Quartet in episode two, his First Symphony in episode five, and a defective recording of his Tragic Overture later in the series.

The final scene, showing Matt Murdock waking with a nun by his side, is a direct homage to a panel from the 1986 Daredevil comic arc 'Born Again,' one of Ramirez's favorite panels, with the nun's call for 'Maggie' hinting at Murdock's mother.

The Hand's search beneath Midland Circle is revealed to involve the skeleton of a dead dragon, tying back to a first-season Daredevil plot point where the villain Gao sells a drug made from crushed dragon bone.

Analytics firm Jumpshot determined The Defenders was the least-viewed Marvel Netflix series and had the steepest week-over-week viewership drop of any of them, even though Netflix reported it was the third most 'Binge Raced' original series globally at release.