The surnames of most main characters were taken from well-known English serial killers, including Harold Shipman, Fred West and Peter Sutcliffe; Ruth Jones said they hoped viewers wouldn't notice at first so that the realization would be 'even more delicious'.

James Corden got the idea for the show at a wedding reception and developed it with co-writer Ruth Jones, whom he had met while filming the ITV drama Fat Friends; the concept was inspired by the real-life story of Corden's friend Gavin, who met his wife over the phone at work.

The creators originally pitched the idea to the BBC as a one-off play titled 'It's My Day', but the BBC asked for a full series instead.

The roles of Gavin and Stacey were cast via auditions but given almost immediately to Mathew Horne and Joanna Page because of their strong on-screen chemistry, while Corden and Jones wrote the roles of Smithy and Nessa for themselves.

Several roles were written with specific actors in mind: Uncle Bryn was written for Rob Brydon, who had attended school with Ruth Jones, and Pam was written for Alison Steadman, who had also worked with Jones on Fat Friends.

The role of Dawn was written for Julia Davis, with whom Jones had previously worked on her sitcom Nighty Night, while Adrian Scarborough was cast as Pete after appearing alongside Corden in the play and film The History Boys, which also led to several of Gavin and Smithy's friends being cast from that production's actors.

The series was filmed largely in Cardiff, standing in for Billericay, and around Barry and nearby areas like Dinas Powys, Sully and Penarth; Gavin's on-screen house at '23 Limetree Avenue' in Billericay was actually filmed on Laburnum Way in Dinas Powys, Wales.

Matt Lucas made a guest appearance in the fourth episode of series one, and his name reportedly helped secure filming permissions for the locations used in Barry.

The 'Barry Islands in the Stream' Comic Relief sketch, featuring Bryn and Nessa performing with real-life singer Tom Jones and Bee Gee Robin Gibb, was released as a charity single and debuted at number one on the UK Singles Chart in March 2009.

The 2019 Christmas special drew 18.49 million total viewers, making it the most-watched non-sporting broadcast in the UK in a decade and the most-watched comedy in 17 years, while the 2024 finale became the most-watched scripted show in over two decades.

Gavin & Stacey was named the 17th-greatest British sitcom of all time in a 2019 Radio Times poll and was the most-nominated show at the 2007 British Comedy Awards.

Multiple American remakes were attempted without success, including versions developed for NBC and ABC, and Fox's 'Us & Them', of which only six of thirteen ordered episodes were produced and none ultimately aired.