Smith was born in Newarthill in Motherwell, and she continues to live in Glasgow. She was awarded the honorary degree of Doctor of the University by the University of Glasgow in 2008. She attended Braidhurst High School in Motherwell, and trained at the Royal Scottish Academy of Music and Drama and Queen Margaret University, Edinburgh.
In 1984, she made her TV debut on the BBC Scotland comedy Laugh??? I Nearly Paid My Licence Fee, however her first major television appearance came in 1986 as a star on the BBC sketch show Naked Video. Made by BBC Scotland, it was shown throughout the UK on BBC Two. In between seasons of Naked Video, Smith also starred in Scottish sitcom City Lights, which ran for four years on the BBC.
Smith is best known for her role as Mary "Mary Doll" Nesbitt in the BBC sitcom Rab C. Nesbitt, a series based on characters in a Naked Video sketch. Launched in 1990 and set in Glasgow, the show was a cult hit, and ran for nine years on BBC2. The show was revived for a Christmas special in 2008, two new series in 2010 and 2011, and a New Year special in 2014.
Smith has appeared in the BBC dramas Two Thousand Acres of Sky and 55 Degrees North, performed alongside Helena Bonham Carter in the British film Women Talking Dirty, and toured Scotland with her stand-up comedy show.
In 2010 she took part in an STV tribute to Scottish actor Gerard Kelly. In January 2011 she appeared on Celebrity Mastermind with singer-songwriter Joni Mitchell as her specialist subject. She finished second on the programme.
For many years she was a regular in pantomime at the Kings' Theatre, Glasgow, starring alongside Gerard Kelly in performances such as Aladdin, Mother Goose and Sleeping Beauty. More recently, she has appeared in her own seasonal show, 12 Nights of Christmas at the Oran Mor, Glasgow.
She has also toured Scotland in straight plays, notably with Andy Gray, in The Woman Who Cooked Her Husband, Two and The Rise and Fall of Little Voice. Other notable Scottish theatre roles include The Steamie, Guys and Dolls and Shirley Valentine. She has also performed in new works at the Tron Theatre, Glasgow and the Traverse Theatre, Edinburgh.
In September 2008 she began touring the UK in a stage version of the hit British film Calendar Girls, along with Lynda Bellingham, Patricia Hodge, Siân Phillips, Gaynor Faye and Brigit Forsyth. The show opened in London's West End at the Noël Coward Theatre in April 2009. The original cast left the show at the end of July 2009 but Smith returned in a different role as part of a national tour in 2010.
Since 2009, Smith has starred in Christmas pantomimes at His Majesty's Theatre, Aberdeen. In 2017 she will return to the King's Theatre, Glasgow.
In 2012, she played Scottish singer Susan Boyle in the musical I Dreamed a Dream (which she co-wrote with Alan McHugh), based on Boyle's life and rise to fame. There were plans to tour the show in Australia in 2013 but these plans were cancelled.
In 2016 Smith toured Scotland as Miss Hannigan in the musical Annie. In 2017 she will tour in a musical version of Kay Mellor's Fat Friends.
Until 2009, Smith wrote a weekly column in the Sunday Mail newspaper. In May 2007, Elaine C. Smith declared her support for Scotland becoming an independent nation by aligning herself with the Scottish National Party. Previous to that, she had been a member the Labour Party but left due to Labour's failure to publicly back the 1984–1985 miners' strike.
In August 2007, she was appointed to the Scottish Broadcasting Commission established by the Scottish Government; and, in October 2007, she appeared in an episode of the Jennifer Saunders sitcom The Life and Times of Vivienne Vyle.
She is a supporter of numerous charities, including Zero Tolerance and Relationships Scotland. She is the patron of the Women and Girl's Programme at Celtic FC.
In late 2009 her autobiography, Nothing Like a Dame (ISBN 1845964551), was published.
Since 2015 Smith has presented a documentary-style show entitled Burdz Eye View, in which she tours Scotland with her comedy act and talks about Scottish life and culture. The show is broadcast by STV.
In 2015 Smith had a part in the third series of Kay Mellor's BBC drama The Syndicate.
In 2016 she began starring in the BBC Scotland sitcom Two Doors Down.