Knightfall was picked up by History in January 2016 as a straight-to-series order of 10 episodes, executive produced by Jeremy Renner, and conceived by his production partner Don Handfield along with writer Richard Rayner.

Showrunner Dominic Minghella said that the Swedish film Arn – The Knight Templar was one of the main inspirations for the series.

Mark Hamill joined the season 2 cast as Master Talus, a veteran Templar training younger knights; reviewers praised his performance, with one noting the 'barely recognizable Star Wars icon carries every scene in which he appears'.

Genevieve Gaunt took over the recurring role of Princess Isabella in season 2, replacing Sabrina Bartlett who played the character in season 1.

Filming began with three days of shooting in Dubrovnik, Croatia during the last week of June 2016, using the Walls of Dubrovnik's Fort Lovrijenac to depict the Siege of Acre, with over 140 Croatian film workers involved.

The series was shot primarily in Prague at Barrandov Studios, chosen partly because of the quality of the 15th-century interior sets the studio had previously built for the series Borgia.

On August 26, 2016, a fire broke out at the Barrandov Studios backlot, destroying the exterior sets for Knightfall and causing an estimated 100 million CZK (about US$4.5 million) in damage; only a small part representing a medieval city survived, and shooting resumed at another city location the following Monday.

Lead actor Tom Cullen underwent a two-and-a-half week sword-fighting 'boot camp' with French stuntman and fight choreographer Cédric Proust, despite not having swung a sword in eight years.

Historical consultant Dan Jones defended the series' inaccuracies as dramatic license, noting that the quest for the Holy Grail would have been recognized as myth even by people in the Middle Ages.

In May 2017, A+E Networks partnered with Titan Publishing to develop original novels and an eight-part comic book series based on Knightfall, and in 2019 a tie-in novel titled The Infinite Deep was released by author David B Coe.