Sparkes was born in Swansea, Wales. He began his working life at Lloyds Bank in Mumbles. After a time as an English Teacher, in the 1980s, he turned to comedy and moved to London, becoming an established performer in the first years of London's alternative cabaret circuit alongside Alexi Sayle, Jo Brand, Paul Merton and Rick Mayall.
He was one of the team behind the Channel 4 Sketch show Absolutely, which ran for four years between 1989 and 1993. Following an award-winning radio special, a new series for BBC Radio 4 was commissioned for broadcast in September 2015.
Barry Welsh is Coming was a long-running comedy series for ITV Wales. As well as playing Barry Welsh, the hapless host of a chat show, Sparkes also plays other characters within the programme, such as pub singer Gwyn, Old Mr Ffff and Fishguard news reporter Hugh Pugh. Although the series ended in 2004, it returned in 2007 for a series of one-off specials.
In 2005 he performed at the Edinburgh Festival Fringe in Absolutely Presents John Sparkes and Pete Baikie with his colleague from Absolutely.
Sparkes starred in the Sketch show Naked Video, where he played Siadwel, the geeky poet who wore an anorak and glasses. The character also appeared when Sparkes was part of the BBC Radio 4 comedy programme Bodgers, Banks & Sparkes. After killing off Siadwel in Naked Video, Sparkes revived the character in 2014 for a new series of radio shows for BBC Radio Wales, which was recommissioned a year later.
