Fearnley was born on 23 March 1981 in the New South Wales town of Cowra as the youngest of five children. He was born with sacral agenesis; he is missing certain parts of his lower spine and all of his sacrum. At the time of his birth, doctors did not believe he would live longer than a week. He grew up in the small New South Wales town of Carcoar. At school, he took part in all sports including athletics and rugby league. He won his first athletics medal in the high jump. He took up wheelchair racing at the age of 14 and took it to an elite level at the age of 17.