Writing primarily for a readership of older children and young adults, Caroline Macdonald created stories that frequently featured 'young people' who were 'lonely and physically or emotionally isolated from others'. The author spent her formative years in New Zealand, growing up as the youngest (by eleven years) of four siblings and this childhood experience had a lasting resonance for Macdonald whose writing reflected a 'particular interest in isolated characters'.
The daughter of an electrical engineer and a librarian, Macdonald attended Stratford primary and technical high schools. Weekends and summer holidays were spent at Oakura, where the family had a beach house; this location became the setting for her first published work, the young adult novella, Elephant Rock (1983). Macdonald studied in Wellington and became an accountant, and although she held various jobs her main vocational experience was in the book trade. While still in New Zealand she worked as an editor for Oxford University Press.
Moving to Australia in 1982, Macdonald wrote Elephant Rock during a period of unemployment in Tasmania. The novella was published the following year and its success gained the author popular recognition. Settling in Adelaide (South Australia) during the early 1990s, Macdonald began writing full-time with a particular focus in the genres of science fiction and fantasy. Even though all Macdonald's books were written while she lived in Australia, the author kept strong ties with New Zealand and her homeland often provided the setting for her stories. A further inspiration for her work, particularly the novel Speaking to Miranda (1990), was her daughter Erica who was newborn when Macdonald gave her up for adoption in 1967. Macdonald began to search for Erica during the 1980s and in 1989 mother and daughter were reunited. They went on to establish a close friendship.
Macdonald's stories have been anthologised in numerous publications. She has also published primary school readers and a selected work of six plays, Act It Out (1988), intended for secondary school ESL students. While living in Adelaide, Macdonald worked as an editor of teaching material, was on the Board of the S. A. Writers' Centre (1994-1995), and in the mid-1990s lectured in creative writing at the University of South Australia.
When Macdonald died of cancer at the age of forty-eight, she left at least two unfinished novels.