Gannon's career started, in 1987, when she entered the Richard Burton Award for New Playwrights. Her play,
Keeping Tom Nice, about a disabled boy whose father commits suicide, earned her the award and a six-month writer-in-residence post at the
Royal Shakespeare Company. In 1988,
Keeping Tom Nice was shown at the
Almeida Theatre in London, and, in 1989, it was shown as a BBC TV
Screenplay starring
Linus Roache. As well as creating longer series, including
Peak Practice, Gannon has written several single or short run dramas for television, including
Dad,
Tender Loving Care,
Trip Trap,
The Gift,
Big Cat,
Pure Wickedness and
The Children. In 2012, Gannon wrote the
one-off BBC Two drama
The Best of Men, which told the story of the first
Paralympic Games, and starred
Eddie Marsan and
Rob Brydon. She was the lead writer and creator of the 2013 BBC One drama series
Frankie. In 2008 Gannon, criticised the BBC, saying that delays in commissioning programmes threaten writers and producers. In 2020, Gannon published her memoir,
The Amazingly Astonishing Story. It was shortlisted for Wales Book of the Year 2021. In 2022, Gannon published a
writing guide,
Do Drama: How to stop watching TV drama. And start writing it. ==Awards==