William Sylvester Walker was the son of a squatter, William B. Walker, and a nephew of Rolf Boldrewood, who was his mother's brother. He was born at Heidelberg, and travelled extensively around Australia gaining firsthand knowledge of station life and mining, including at 'Merangle' on the Lachlan (owned by two uncles, Molesworth Greene and Robert Massie) and on the Paroo in Queensland, with his brother and his uncle Sylvester Browne. He uses these experiences in his fiction, locating his stories from the north-west of Australia to the east coast of Queensland and New South Wales. Walker also lived in New Zealand for fifteen years, where he worked as a journalist and adopted the pseudonym 'Cooee', and worked in the diamond mines in South Africa. He later settled in Scotland, having married a Scottish woman.
His works are set mainly in the 1860s and 70s and include short stories, sketches and novels. His Australian settings range from cattle stations to gold mines and the pearling industry. Although inclined towards melodrama, his writing draws detailed pictures of the lives of miners, settlers and pioneers.