The development began with a team of 60 people – later expanded to around 80 – many of whom worked on Dontnod Entertainment’s previous project Life Is Strange. For a short time, the developer considered to set the game in 1950s America, but to inspire a more gothic mood it was discarded in favour of the 1918 London Spanish flu pandemic. The paintings of Phil Hale influenced the art style, also for the purpose of atmosphere. Television series Casualty 1900s and The Knick were turned to for medical information. Dontnod conducted field research on the setting by visiting London and taking photographs, but since the city had been largely rebuilt, history books and documentaries concerning Whitechapel, the London Docks and the Isle of Dogs were also consulted. Events surrounding the period were studied using both factual and fictional reference points[a] to create the visuals, realised with photorealistic lighting, and post-processes running on the Unreal Engine 4. The killing of innocents in the game as the price for immortality is intended to explore the dualism of the protagonist’s survival as a vampire while also being a doctor, either by adhering to the Hippocratic Oath or capitulating to the vampiric nature.
In August 2016, Dontnod had overcome the major obstacles in developing the game on Xbox One and assured that there would be no downgrades despite its hardware disadvantages.