At the age of 13, when living in Australia with his family, O'Rourke was given his first guitar by a priest in Kyabram who recognised his potential and love for music; Hence the title of his debut album "Since Kyabram", which was released in October 2004.
The album's launch took place over three sold-out nights in Whelan’s of Wexford St, Dublin and was broadcast live on national radio. It entered the official Irish album charts at Number 5 and was the only new Irish entry in the Top 75 album chart that week. "Since Kyabram" quickly went gold, then achieved platinum status. Since the release of the album, O'Rourke has completed two sell-out nationwide Irish tours, with the second one culminating in a full capacity show in Dublin's Olympia Theatre in March 2005.
O'Rourke has been among the few solo performers selected to appear on both the second and third TV series of Other Voices. O'Rourke tracks were included on the #1 selling compilations Even Better than the Real Thing Vol. 2 and Even Better than the Real Thing Vol. 3 in aid of The National Children's Hospital in Tallaght and Tsunami Relief respectively.
Other career highlights include performing at the first "Irish Woodstock" in Inistioge, Kilkenny, playing guitar with Bic Runga on her European tour, opening multiple shows for Planxty during the concerts at Vicar St., and being on the same bill as Bob Dylan for three consecutive shows. More recently O'Rourke played guitar for Snow Patrol during their Oxygen Festival performance in Ireland during July 2007. Snow Patrol's lead singer, Gary Lightbody, gave a very positive review of O'Rourke's forthcoming second album a preview copy of which, he revealed, the band had been listening to backstage.
O'Rourke has attracted comments from Paul Weller, Rolling Stones guitarist, Ronnie Wood, and from Paul Brady who describes O'Rourke as a "most talented singer-songwriter... [possessing] a rich, soulful, musical voice and a brilliant instrumental ability"; Eddi Reader once said that he was "one of the finest songwriters on the planet".
In October 2007 Declan released his second album, 'Big Bad Beautiful World' after performing selected tracks on Irish radio.
Galileo, the first single from the album, was voted "Single of the Fortnight" and hailed by John Walshe from Hot Press as "a deliciously old world ballad…".
In Q Magazine, Paul Weller was asked what song in the last 20 years did he wish he’d written and he chose Galileo.