Nimmo's love of books was evident at an early age. At nine years old she had already read all of the books in her school's junior library and was begging for permission to join the senior library. Jenny realized early in her childhood that writing stories could be as much fun as reading them. So began her years of writing and thrilling her friends with creepy stories
Before Nimmo established her career as a writer, she worked in television adapting other people's stories for television programs. When she tried her hand at writing her own television program, her producer suggested that with some added length it would make a wonderful novel. This novel became her first book, The Bronze Trumpeter, which was published in 1975.
Nimmo conducts a simple life of writing. She lives in an old water mill in Wales and begins her day of writing only after the chickens, rabbits, and cats have all been fed. She writes her stories out in longhand, editing as she goes. Then, once her manuscript is complete, she types it up on a computer for her publisher's review. During the summer she puts down her pencil to help her husband run a summer school at their home.