Mackin was married with five children and worked as a shipyard labourer in Hebburn, Wallsend and Blyth. He served as a private in the Royal Northumberland Fusiliers during the First World War and was wounded on the first day on the Somme. Mackin was killed during the Battle of Vimy Ridge on 9 April 1917. He was buried in Roclincourt Military Cemetery.