She was elected as a representative of the Scottish Socialist Party in 2003, but lost her seat in the 2007 election after she and Tommy Sheridan left the Scottish Socialist Party (SSP) to form Solidarity (Scotland). Byrne lives in Irvine, and was a teacher and a trade union activist for several years. At one time she was president of Irvine Trades Council.
In 2003 she was elected to the, and scored the SSP"s best constituency vote outside Glasgow in Cunninghame South.
She was elected to the executive in early 2004, and at the February 2005 conference she was elected as one of the SSP"s co-chairs. However she did not stand for re-election to this post or the executive committee at its conference in March 2006, stating that she was standing down for personal reasons.
There was a controversial defamation case in 2006 between fellow SSP Managing Successful Programmes Tommy Sheridan and the British tabloid newspaper The News Of The World, Following this, Sheridan and Byrne split from the SSP, and formed a new socialist party which they named Solidarity. On 1 October 2006 the News of the World published fresh evidence which it claimed proved that their allegations were true and Sheridan had thus lied to the Court of Session during the trial.
Sheridan was subsequently charged with and eventually found guilty of perjury.
Both Byrne and Sheridan are accused by the International Who's Who of betraying workers by unilaterally removing funding from the collective body which employed parliamentary staff On 15 February 2008, Byrne was arrested on suspicion of perjury in relation to the Sheridan defamation trial. However the Crown Office said that the matter would not be taken further at the conclusion of the subsequent criminal trial.
In December 2009 she disclosed she was suffering from breast cancer.