After qualifying as a doctor in 1983, Evans worked in medicine in Newcastle for four years before a brief period in stand-up, beginning with an ensemble review called "Wire Less Wireless" which played in some of the pubs in Newcastle. Evans joined BBC Radio where she was a producer of comedy programmes before migrating to television. She has produced and/or directed such shows as ''Father Ted'' (for which she won a BAFTA for best comedy), ''Room 101'', ''The Kumars at No. 42'', ''TV Heaven, Telly Hell'', ''Crossing the Floor'' (for which she won an Emmy for best drama) and ''Have I Got News For You''.
Evans has written six novels for adults: ''Spencer's List'', ''Odd One Out'', ''Their Finest Hour and a Half'' (now filmed as ''Their Finest'') ''Crooked Heart'' (which with ''Their Finest Hour and a Half'' was long-listed for the Baileys Women's Prize for Fiction), ''Old Baggage'' and ''V for Victory''.
For children, she has written ''Small Change For Stuart'', shortlisted for the 2011 Costa Award for Children's fiction, the 2012 Carnegie Medal, and the 2012 Branford Boase Award. ''Small Change for Stuart'' was published in the United States as ''Horten's Miraculous Mechanisms'', and the sequel, ''Big Change for Stuart'' (''Horten's Incredible Illusions'' in the U.S.) was published in 2012. Another book for children, ''Wed Wabbit'', was published in 2017 and shortlisted for the 2017 Costa Book Awards and the 2018 Carnegie Medal.