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.
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.
In late 2009, her autobiography, Nothing Like a Dame (ISBN 1845964551), was published.
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.
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.
