 His mother was Annabella, Hyde, and his father was John Simpson Mackennal, a "prominent Melbourne artist and sculptor".Bertram's brother Horace John Mackennal (died 28 June 1949) would go on to be a prominent architect who was responsible for the design of many large architectural projects in Victoria in his capacity as Commonwealth Works Director for Victoria (1912–1939).John Mackennal provided Bertram his early training which was followed by studies at the school of design at the Melbourne National Gallery which he attended from 1878 to 1882.