After studying at the Royal Academy of Music, James Watson was appointed Principal Trumpet of the Royal Philharmonic Orchestra by Rudolf Kemp. He held the same position with the London Sinfonietta and the Nash Ensemble. After five years with the RPO he left to concentrate on playing solo and chamber music, notably leading the Philip Jones Brass Ensemble. From 1983 to 1990 James was the Principal Trumpeter at the Royal Opera House, Covent Garden.

James returned to brass bands in 1987, more particularly to the Desford Colliery Brass Band – with whom he had played principal cornet during his early teens – and led them during four visits to the National Championships between 1987 and 1991. he then joined the Black Dyke Mills Band, winning the open in 1992 and 1995, achieving second place in 1993 and 1994, and winning the National Championships in 1995. He also commissioned several pieces for brass band by composer Nigel Clarke.

As Professor of Trumpet and Head of Brass Ensembles at the Royal Academy of Music, James was honoured with an Academy Fellowship in 1989. He subsequently became an Honorary Fellow of the London College of Music and Media, and divided his time between teaching and a very busy performing schedule. He also played with the London Symphony Orchestra and its brass ensemble. In addition he was, in 1996, appointed as Artistic Director and Principal Conductor of the National Youth Brass Band of Wales, and in the same year was awarded the Iles Medal by the Worshipful Company of Musicians.

James was Head of Brasss at the Royal Academy of Music, London from 2001 until his untimely death at the age of 59 in February 2011.