The series was created by Russell T Davies as part of the Doctor Who franchise (the Whoniverse), first reported in July 2024 by Deadline Hollywood as set to begin filming in September, though Davies confirmed at San Diego Comic Con that production would actually start in August.

Russell Tovey and Gugu Mbatha-Raw, who lead the series, had previously appeared in Doctor Who itself playing different characters, Alonso Frame and Tish Jones respectively.

Colin McFarlane reprises his role as General Austin Pierce, a character first introduced in the third series of Torchwood fifteen years prior to this spin-off.

According to writer Pete McTighe, Davies had already devised the series' concept and scripted its first episode before writing the Doctor Who 60th anniversary specials, and only invited McTighe to co-write the rest of the spin-off in 2023 after McTighe delivered his first Doctor Who episode draft.

Davies initially stated he had co-written the fourth episode with McTighe, but was subsequently not credited as co-writer on the episode itself.

Unlike the usual two to three production blocks for a five-episode series, all episodes of The War Between the Land and the Sea were filmed in a single block, with the first read-through for all five scripts held on 19 August 2024 right after Doctor Who series 15 wrapped filming.

Filming took place across numerous locations in south Wales (including Barry, Atlantic Wharf, Cardiff City Hall, National Museum Cardiff, and Merthyr Mawr), as well as in Bristol, Mallorca, New York, aboard the research vessel RRS James Cook, and concluded on 9 December 2024 at the Pinewood Studios Underwater Stage.

Composer Lorne Balfe scored the series, and the soundtrack album included a cover of David Bowie's 'Heroes' performed by Alison Goldfrapp and Balfe, released as a single through Goldfrapp's own label A.G. Records.