Hennessy released his first album in 1972, but his big break came with the release of The Rehearsal in 1992, which went triple platinum and established him as a best-selling artist.
While Christie enjoyed the success of his own records, he also dabbled in production, and wrote music for film and TV.
His tracks 'Don't Forget Your Shovel' and 'All The Lies That You Told Me' were made famous by Christy Moore and Mary Black respectively, while artists like Clannad and Nizlopi have also covered his songs.
The 62-year-old had been touring in Ireland this year, but had to cancel recent dates due to illness. He passed away in London this morning.
A statement on his official website says:
"It is with great sadness that we announce that Christie passed away this morning.
We just want you all to know how much that Christie appreciated your love and support over the years. He will be sadly missed by all."