Hemsley was born in Coalville, Leicestershire, and attended Ashby de la Zouch Grammar School.
[2] He moved to London and became a pupil of Lucie Manén, and also served as a Vicar Choral at St Paul's Cathedral.
[1] In 1960, Hemsley created the role of Demetrius in Britten's A Midsummer Night's Dream with the English Opera Group at Aldeburgh.
In 1965, he was the baritone soloist in only the second UK performance (and only the fourth performance in the work's history) of Delius's Requiem, in Liverpool, with the Royal Liverpool Philharmonic Orchestra under Charles Groves.
Hemsley was a notable interpreter of German music, such as Beckmesser in Wagner's Die Meistersinger von Nürnberg.