His first commercial single "Dublin Town" was released in 1997, and reached number 18 in the Irish music charts. The Irish music magazine "Hot Press" praised the single, remarking that it was "..an underground anthem for disaffected youth and closet balladeer alike". His first full length album, titled "They Don't Teach This Shit In School" was released in 2000 and contained a re-recorded version of this song.

His next release, in 2002, the "Negative Vibes EP" featured Sinéad O'Connor on the title track and led to an invitation to support Sinéad on her 2002/2003 Irish, UK, and European tour.

Damien's second full-length album, "Seize the Day", was released in May 2003 in Ireland on Clear Records via Sony and entered the charts in its first week of release at No. 5. It has since achieved double-platinum sales. Released in May 2004 in the UK on IRL, the album was awarded "CD of the Week" in the Sunday Times and received enthusiastic reviews in National and music press.

In 2004 Dempsey toured extensively headlining his own shows as well as supporting Bob Dylan during the Irish leg of his European tour and making his debut appearances at The Fleadh and Womad.

He has earned the support of his peers, particularly Morrissey, who invited Damien to support him on various UK and Irish dates as well as his autumn 2004 US tour. Morrissey went on to sign Damien to his label (Attack), and "Seize the Day" had its U.S. release in October 2004.

His third album, "Shots", simultaneously released in Ireland and the UK in March 2005 entered the Irish album charts at #1.

Dempsey flirted with controversy during his Oxegen 2006 performance. On the main stage on Saturday afternoon, the singer sensationally suggested that Patrick Pearse would be "turning in his grave" at the state of modern Ireland.