Damien started out as an outstanding gaelic footballer for Cork up until Minor level before deciding to focus on Soccer. He originally transferred from Cork City to Leicester City in 2000 as a left-back, but he has proved his versatility since with a variety of clubs. At Hull City he lined out at centre-back and midfield and enjoyed back-to-back promotions. He then moved to QPR, but has been with Ipswich for the last two seasons.
Damien has proven to be particularly useful at setpieces, and was originally called into Giovanni Trapattoni's squad in May 2008. He played his first 90 minutes against Northern Ireland in Ireland's 5-0 Carling Nations Cup win.
He helped Crystal Palace to promotion via the play-offs in 2013 and was capped against Georgia and Spain in end of season friendly matches.