McLynn was born in Sligo but grew up in Galway. She studied History of Art and Modern English at Trinity College, Dublin, but was more heavily involved in Trinity's Dublin University Players, the college's drama society. She graduated with an MA.
Although McLynn was in her early thirties when playing Mrs Doyle, makeup was used to make her look far older to fit the character's profile. She received a British Comedy Award for her performances in 1996. The award was presented to her by British prime minister Tony Blair.
Other televised appearances have been in sketches on Bremner, Bird and Fortune, and numerous panel shows, including Just a Minute, Have I Got News For You, and If I Ruled the World. In 1999, she appeared in the film adaptation of Angela's Ashes. She has also appeared in Jennifer Saunders' Jam & Jerusalem. In the late 1990s she was recruited to play Mrs. Doyle for a UK advert for online Tax returns by the Inland Revenue and became infamous for the phrase 'Go Online'.sup>
McLynn also got an unusual opportunity during her only appearance on They Think It's All Over, the BBC1 TV show. Fellow guest panellist Gabby Yorath requested that she be allowed to take part in the Feel the Sportsman Round (which was unusual at the time as the team captain usually did this along with the other, regular panelist). Yorath was granted her request, and Pauline (who was on the opposing team) was offered the chance to don the blindfold herself and take part with her team captain Rory McGrath. She was only the third woman to do so at the time.
McLynn was critically acclaimed for her performance in the 2005 film Gypo, receiving an Irish Film and Television Award nomination for Best Actress.
McLynn has also featured on Metro Radio, a radio station in the North East. McLynn did the "Mrs. Doyle" voiceover on an Advert for a local estate agents and letting agents in newcastle Clarke Holland.
McLynn played Mary Whyte in the BBC's 2013 sitcom Father Figure. On 12 May 2014, she joined the cast of EastEnders as Yvonne Cotton], the mother of Charlie Cotton and ex-daughter-in-law of Dot Branning.
McLynn is the author of seven novels. These include Missing You Already, Bright Lights and Promises, Summer in the City, The Woman on the Bus, Right on Time, Better than a Rest and Something for the Weekend.
McLynn is married to theatrical agent Richard Cook. She is a patron of the children's charity World Vision Ireland and is vice-president of Friends of Innisfree Housing Association. McLynn is a big fan of the Premier League football team Aston Villa. She says her best moment supporting Villa came in 1996 when she watched her beloved team beat Leeds United in the League Cup final with her Father Ted co-star Ardal O'Hanlon who is a big Leeds supporter.