Netflix approached writer Kim Eun-hee for a new project after her previous series Signal ended, and after she successfully pitched the zombie-Joseon concept, Netflix officially ordered a first season on March 5, 2017.

Kim Eun-hee began developing the story in 2011, but initially thought it too difficult to adapt for television, so she first created it as a webcomic titled The Kingdom of the Gods with illustrator Yang Kyung-il in 2014 before it became the Netflix series.

The writer has cited the success of Train to Busan as a turning point that revitalized interest in zombie stories in Korean media, which helped make the Kingdom project viable.

Actor Song Joong-ki was courted for the lead role of Lee Chang but declined, and the part eventually went to Ju Ji-hoon.

Jun Ji-hyun revealed she was such a big fan of Kingdom that when she privately met writer Kim Eun-hee before being offered a role, she said she would even be willing to appear as a zombie in the show.

The production significantly overspent its budget, with each episode costing more than $1.78 million, forcing the first two seasons—originally planned for eight episodes each—to be shortened to six episodes.

The production was marked by tragedy: a member of the art team died from overwork on January 16, 2018, and a staff member died in a car accident during filming of the second season on March 14, 2019.

On January 7, 2021, a castle set built for Kingdom: Ashin of the North caught fire after a staff member used a torch lamp to melt snow, destroying parts of the set though no one was injured.

Filming for the first two seasons took place in Seoul, Gyeonggi Province and North Gyeongsang Province between 2018 and 2019, while the special episode Ashin of the North was shot on Jeju Island in 2020.

Kim Eun-hee said she designed each season around a specific theme: hunger and starvation for the first season, and blood/lineage obsession for the second, using the zombie plague as a metaphor for political corruption and inequality.