Born in Bream,[1] in the Forest of Dean, Gloucestershire, he was educated at Whitecross School; and the University of East Anglia, graduating with a law degree in 2000.

[6] Comments on Bebo and other internet sites, including death threats and personal abuse, were condemned by the International Rugby Board and New Zealand Prime Minister Helen Clark.

He was appointed in 2008 to take charge of his first Heineken Cup knockout match, between Stade Toulousain and Cardiff Blues at Le Stadium on 6 April 2008.

[14] On 22 December 2017, Barnes broke the all time Premiership appearances record (191) for a referee while officiating Worcester Warriors 23–8 victory over London Irish.

Joining Barnes were compatriots Karl Dickson and Matthew Carley as assistant referees, and Tom Foley as the television match official.

[20] Barnes' autobiography, Throwing the Book, written with Ben Dirs, with an audiobook version narrated by Rich Keeble, was released by Hachette on 9 November 2023.