Fienberg was born in 1956 in England before moving to Australia at the age of three. She has worked as an editor for School Magazine. In 1988 her first work was published, entitled Billy Bear and the Wild Winter. In 1989 Fienberg released her first novel, The Nine Lives of Balthazar. She has won the Younger Readers in 1992 for The Magnificent Nose and Other Marvels and has been a short-list nominee on four other occasions. Fienberg has also won the Alan Marshall Award for Children's Literature in 1993 for Ariel, Zed & the Secret of Life and the 2003 Aurealis Award for best children's short fiction for Tashi and the Haunted House. She has also been a Aurealis Award finalist on four other occasions.