Stanner was born at Watson's Bay, Sydney on 24 November 1905, the second son of Andrew Edwin Stanner and Mary Catherine Stanner (née Hanley). He was 3 years old when his father died. He was educated at state schools and won a bursary to Parramatta High School (1919–21), but was unable to stay on after the Intermediate Certificate for financial reasons. Stanner worked for two years in a bank and matriculated by private study. He worked as a journalist while studying at the University of Sydney, initially for the Cumberland Argus. In 1927 Stanner obtained full-time work as a reporter for the Sydney "Daily Guardian" for Frank Packer, the first of a number of posts in journalism which financed his studies in Australia and England.