Guy is a renowned trumpet player and composer. He started playing the trumpet at the age of twelve, and within a year had joined NYJO. After lessons from Clark Terry in 1975, Guy went on in the 1980s to play with John Dankworth, Gil Evans (with whose orchestra he toured and recorded in 1983), Lena Horne and Bobby Watson.
From 2008 to 2014 Guy was the Musical Director/Arranger for the opening gala concert Jazz Voice: Celebrating a Century of Song at the annual London Jazz Festival. He was also the Musical Director/Arranger on a number of BBC Radio 2 Friday Night is Music Night shows featuring the Guy Barker Jazz Orchestra with the BBC Concert Orchestra.
He was appointed Member of the Order of the British Empire (MBE) in the 2015 New Year Honours for Services to Jazz.