He was the son of the late William George Milligan and Elizabeth Milligan, of Ballymascanlon, Co. Louth.
In 1901 the family were living with a Jane McKenney in house 2, Culfore, Ballymascanlon. Jane is described as the head of family. William George Milligan and his two children are living with McKenney.
By 1911 Milligan is recorded as boarding in house 24, Drumcar, Co. Louth.
He was serving with the 7th Bn. Royal Inniskilling Fusiliers as a 2nd Lieutenant when he was killed in action on 29th April 1916 aged 19. Milligan is buried in the Philosphe British Cemetery, Mazingarbe, Pas De Calais, France.