He studied at the Athenaeum School of Music, then moved to London and joined the band of Jack Hylton from 1929 to 1936.
Munn also played on recordings with Spike Hughes (1932) and Benny Carter (1936) during this time.
He played with Stephane Grappelli in 1943 and George Chisholm in 1944, then led his own ensemble at the Orchid Room in Mayfair from 1945 to 1948.
He co-founded the BBC program Jazz Club in the 1940s with producer Mark White and clarinettist Harry Parry.
He also Played With Victor Silvester becoming a member of Victor Silvester's Jive Band From 1948 to 1949, Munn directed the Maurice Winnick Orchestra at Ciro's club in London, England, and subsequently led the house band at the Imperial Hotel in Torquay for three decades, from 1949 to 1979.