Rina Satō, Satomi Arai, Aki Toyosaki, and Kanae Itō reprise their roles from the previous two seasons of A Certain Scientific Railgun.

Azumi Asakura joins them as Shokuhō, whom she also voiced in the first and final episodes of A Certain Scientific Railgun S. Production of the third season was announced in October 2018, with Nagai returning as the director.

Several episodes got delayed due to the COVID-19 pandemic, which caused the season to conclude on September 25, 2020, instead of June as was originally scheduled.

[40] With the announcement of a third season in October 2018, Rina Satō, Satomi Arai, Aki Toyosaki, Kanae Itō, and Azumi Asakura were also confirmed to reprise their respective roles as Mikoto Misaka, Kuroko Shirai, Kazari Uiharu, Ruiko Saten, and Misaki Shokuhō.

[32] Additional cast were confirmed in December 2019, including Kengo Kawanishi as Gunha Sogīta and Miyu Tomita as Mitori Kōzaku.

[41] In February 2020, Konomi Kohara joined the cast as Dolly,[42] as did Atsumi Tanezaki in April as Ryōko Kuriba / Doppelganger.