David Day, born in 1949, is an Australian historian and author. Day has written widely on Australian history and the history of the Second World War. Among his many books are Menzies and Churchill at War and a two volume study of Anglo-Australian relations during the Second World War. His prize-winning history of Australia, Claiming a Continent, won the prestigious non-fiction prize in the 1998 South Australian Festival Awards for Literature. An earlier book, Smugglers and Sailors, was shortlisted by the Fellowship of Australian Writers for its Book of the Year Award. John Curtin: A Life was shortlisted for the 2000 NSW Premier's Literary Awards' Douglas Stewart Prize for Non-Fiction.

His 2013 book, Antarctica: A Biography, offers an engaging account of the frozen continent. Day's latest book, Paul Keating: The Biography, was published in 2015.