Downer was born in
Alexandra, Victoria, Australia, on 4 February 1895, the son of Edwin Harry Downer (died 24 October 1945), a builder, and his wife Mary Ann McMinn (died 13 January 1956). In 1899, the family emigrated to New Zealand and settled in
Feilding, where Downer attended Manchester Street School and the
Feilding District High School, before completing his higher education at
Wanganui Technical College. After leaving high school he obtained a cadetship in 1913 with the
Public Works Department and was employed in their Dunedin office on a number of projects in Otago and Southland. ==World War I==