Catrin Lewis Defis has been involved with television production at BBC Wales since at least 1997. Prior to the arrival of Russell T Davies in Cardiff in 2004, she had already been a line producer on a number of productions, such as Iechyd Da, The Shoe Collector, The Hairy Fairy and Con Passionate — some of which were Welsh-language programs.

Based on her track record, she was given significant responsibilities on Torchwood. During the first series, she was a production manager. In the second, she was elevated to the position of associate producer. Following the departure of Phil Collinson from Doctor Who, she was the full producer of TV: Music of the Spheres. In so doing, she became only the third woman to (line) produce an episode of Doctor Who, behind Verity Lambert and Susie Liggat.

Some counts would place her as the fourth woman to produce a BBC-funded, televised episode of Doctor Who, given Sue Vertue's role on The Curse of Fatal Death.