She was born in Uxbridge in Middlesex. From 1973-78 she went to St Dominic's Independent Grammar School for Girls (St Dominic's Sixth Form College since 1979) in Harrow on the Hill. From 1978-80 she went to the independent Heathfield School in Harrow.
From 1980-91 she worked for the BBC.
She became a presenter for Calendar in June 1991.
Gaynor co-presented the South edition of Calendar from January 2007, however she was redeployed as a newsreader in February 2009, following the merger of North/South editions. Her colleague Christine Talbot took leave from co-presenting Calendar in January 2012, with Barnes acting as her fill-in for the remainder of the year; now as of January 2013 she is a news correspondent.
- Zientek, Henryk (19 November 2008). "Help for entrepreneurs". Huddersfield Examiner. Retrieved 10 August 2010.
- TV Presenter Gaynor Barnes talks to Yorkshire Life Yorkshire Life, 11 January 2010