Smith was born in Erith in Kent in 1958 and was educated at Erith College of Technology (now Bexley College) and at the University of Sheffield where she graduated in English and Drama. She joined a professional theatre company before turning to comedy. In 1987, she won the Hackney Empire New Act of the Year, then known as the New London Comic Award, and performed on the Edinburgh Fringe before breaking into radio comedy.
Many of her early stand-up appearances were benefit concerts staged in solidarity with the British miners during the Miners' Strike in the 1980s. She was a lifelong socialist.
Her first appearances on national radio were on Radio 5's The Treatment in 1997. She was subsequently a regular panellist on The News Quiz and Just a Minute and appeared frequently on I'm Sorry I Haven't a Clue (from June 2001 onwards), Have I Got News for You, Mock the Week, Countdown and QI. She wrote and starred in her own Radio 4 sitcom, Linda Smith's A Brief History of Timewasting. After appearing on Radio 4's Devout Sceptics to discuss her beliefs she was asked by the British Humanist Association (BHA) to become president of the society, a role that she occupied with commitment from 2004 until her death. In 2002, she was voted 'Wittiest Living Person' by listeners to BBC Radio 4's Word of Mouth. In his 2003 book Classic Radio Comedy, Mat Coward called Smith "the funniest woman on radio today".
On 17 November 2003, Smith appeared on the BBC television show Room 101, where she successfully managed to put in "adults who read Harry Potter books", Tim Henman, "Back to School signs that appear in shops" and "posh people". However, she failed to put in Bow ties after host Paul Merton pointed out that Stan Laurel regularly wore a bow tie.
On 27 February 2006, Smith died as a consequence of ovarian cancer at the age of 48. She had been diagnosed with ovarian cancer three and a half years earlier but, not wanting to be thought of as a patient or a victim, she did not want people to know. Before she died she chose that her funeral be humanist and her memorial at the Theatre Royal, Stratford East, on 10 March, was dedicated to the BHA. Her life and work were honoured at the British Academy Television Awards in 2006. The first episode of Dawn French's Girls Who Do: Comedy was dedicated to the memory of Linda Smith.
Two tribute gigs were held in her memory. The first took place on 14 May 2006 at the Lyceum Theatre, Sheffield, In Praise of an English Radical, the second on 4 June 2006 at the Victoria Palace Theatre in London entitled Tippy Top: An Evening of Linda Smith's Favourite Things. In August 2006, Andy Hamilton presented a BBC Radio 4 tribute entitled Linda Smith: A Modern Radio Star. An anthology on CD, entitled I Think the Nurses Are Stealing My Clothes: The Very Best of Linda Smith, was released in November 2006 as was a book with the same name. A tribute show of the same name was aired on BBC Radio 4 on 10 November 2006. Smith's sell-out stage show Wrap Up Warm has been available on CD since November 2006.
Linda Smith was working on a third series of A Brief History of Timewasting before she became incapacitated by her illness. As a tribute the online radio station BBC 7 ran the previous two series, the first all on one day.
The University of Kent holds The Linda Smith Collection as the foundation of the British Stand-Up Comedy Archive. It includes notes, diaries, scripts, audio-visual recordings, photographs, press cuttings, correspondence and publicity material covering her entire life and career. It was deposited at the University of Kent by Linda's partner Warren Lakin in 2013.Sit-Down Comedy (contributor to anthology, ed Malcolm Hardee & John Fleming) Ebury Press/Random House, 2003. ISBN 0-09-188924-3; ISBN 978-0-09-188924-1