Kate Llewellyn grew up at Tumby Bay on Eyre Peninsula, later moving to Adelaide where she trained and worked as a registered nurse at the Royal Adelaide Hospital (graduating in 1958). She also owned and directed two art galleries in Adelaide (1956-1972). Llewellyn enrolled in 1970 at the University of Adelaide, graduating with a BA in history and classics in 1977. She worked on the Unley Planning Study 1978, and in the Women's Advisory Unit of the Premier's Department 1979. Also in 1979, she spent two months in Paris and London.
It was during her undergraduate years that Llewellyn began writing. She won the Bundey Prize for English Verse in 1975. Her first collection, Just a Minute, was published in Sisters Poets 1 (1979), and her first book of poetry, Trader Kate and the Elephants (1982) won the Ann Elder Award. In 1981 she was National Secretary of the Poets' Union. She has read at Friendly Street, Writers' Week, SA Poets' Union readings, schools, colleges and universities. Her poems have been broadcast on Writers' Radio' (5UV).
In 1983 Llewellyn moved to Sydney, and in 1985 moved to Leura, in the Blue Mountains for a time. There she wrote her Blue Mountains trilogy, The Waterlily, Dear You and The Mountain. Llewellyn has also published international travel diaries and a book of essays (The Floral Mother). Divorced in 1972, she has a son Hugh and a daughter Caro who is also an author.