Born into Cardiff's Irish community, Hennessy was used to performance in front of his family by the time his father gave him a guitar aged 13.

Although an apprentice at the time at an electrical contractor, after winning Cardiff Council's 1966 "Spotlight on Youth" talent competition with friend Dave Burns, the pair were persuaded to go professional under the name The Hennessys.

Hennessy's own musical compositions have been recorded by a wide range of artists such as The Fureys, Foster and Allen, Ar Log, Daniel O'Donnell, Diarmuid O'Leary and the Bards and Max Boyce.

In 1978 he was asked to present a programme for the new Cardiff independent radio station CBC, a role he greatly enjoyed.

After CBC's collapse and takeover, in 1984, BBC Radio Wales invited Hennessy to act as a stand-in presenter.