After a short spell at the Cambridge University Press he then joined the BBC in 1935 as a Producer in the Talks Department.
It was under his tenure as Director that interest in television exploded, particularly with the screening of the coronation of Queen Elizabeth II in 1953.
Drawing an audience of an estimated 20 million British and 300 million worldwide viewers – an unprecedented viewership – the Coronation broadcast, when viewed later by the Queen, caused her to knight Barnes on the spot at the BBC's Lime Grove Studios.
Television coverage was now nationwide, although in 1955 the service was faced with the prospect of competition for the first time when the rival ITV network was launched.
In 1927 he married Dorothy Anne, daughter of Henry Bond, Master of Trinity Hall, Cambridge 1919–1929.