In film, she was featured vocalist on "King Arthur" (2004), co-writing the title theme "Tell Me Now (What You See)" with Hans Zimmer and wrote additional music score for "To End All Wars" (2001). In 1995, she duetted with Shane MacGowan with "You're the One" for the movie "Circle of Friends". Brennan has collaborated with many other musicians, including Chicane, Alan Parsons, Bono, Robert Plant, Van Morrison, Michael McDonald from the Doobie Brothers, Bruce Hornsby, Joe Elliott, The Chieftains, Paul Young, Paul Brady, Michael Crawford, Joe Jackson and Ronan Keating.