Margaret John was born in Swansea, as a child she wanted to be a nurse or vet, but she could not stand the sight of blood. She occasionally acted at school with her sister Mair. Spotted while acting in a chapel pagent competition, after an audition John trained at the London Academy of Music and Dramatic Art, graduating in 1950. Margaret John’s first public appearances were at Swansea’s Grand Theatre, where she had small parts in weekly repertoire. Not being a fluent Welsh speaker, she found some productions in Welsh at times challenging. After appearances on radio and in the theatre, she made her television debut in 1956 in a Welsh language drama. Her television roles included appearances on episodes of The First Lady, The Troubleshooters, Softly, Softly, The Mike Yarwood Show, Doomwatch, Blake’s 7, Secret Army, Lovejoy, My Family, High Hopes, The District Nurse, Casualty, and Doctors. On Radio 4, she appeared on Linda Smith’s A Brief History of Timewasting and played Mrs Stone, the school secretary, in the original ten series of King Street Junior from 1985-98. In a career that spanned more than fifty years, she appeared in such television programmes including: Coronation Street, Dixon of Dock Green, Z-Cars, Doctor Who, Little Britain, Emmerdale, Last of the Summer Wine, Crossroads, Gavin & Stacey and The Mighty Boosh. In the early 1980s, she enjoyed a long run on ITV’s daily soap opera Crossroads as doctors’ receptionist Marian Owen. Between 2007 and 2010, she portrayed Doris in Gavin & Stacey.

At the 18th BAFTA Cymru Film, Television and Interactive Media Awards on 17 May 2009, at the Wales Millennium Centre in Cardiff Bay, in a ceremony hosted by Gethin Jones, Margaret John was presented with the Lifetime Achievement Award. In September 2009, John appeared in the graphic short film Cow by director Peter Watkins Hughes warning of the dangers of texting while driving. Also in 2009, John appeared in The Vagina Monologues, before which her last theatre production was in the 1980s in Medea at London’s Young Vic Theatre, opposite Dame Eileen Atkins. John appeared on stage in Calendar Girls at the Wales Millennium Centre from 27 July to 7 August 2010 and at Venue Cymru, Llandudno from 9 to 14 August 2010, alongside fellow Welsh actress Ruth Madoc, playing Lady Cravenshire, the judge of the WI’s cake competition. She also starred in the 2009 low-budget film A Bit of Tom Jones?, a bawdy farce about the Welsh singer’s penis. Her last appearance on screen, broadcast one month after her death, was in the new HBO drama Game of Thrones as Old Nan, an elderly servant in the Stark household, who was slated to be a recurring character.

In March 2010 she appeared in the BBC One Wales programme Margaret John – National Treasure, which featured clips from the last 50 years of television and special guest interviews with, among others, Ruth Jones, Eve Myles and Joanna Page. The programme was broadcast again, in tribute to John, on 5 February 2011. She also featured in a short BBC video in which she cooked Welsh cakes for St. David’s Day. Margaret John died in hospital in Swansea on 2 February 2011 after a brief battle with liver cancer. Just before her death, Swansea University awarded her an Honorary Fellowship for her exemplary and inspiring character in relation to old age, particularly as she continued acting until she became ill shortly before her death. The award was received on her behalf by a nephew, Chris Davies, at a ceremony in the Brangwyn Hall, Swansea.