Second Lieutenant Theodor Milton Pflaum was born on 20 September 1895 in Blumberg (now Birdwood), South Australia, to parents Heinrich Adam Theodor and Mary Jane Pflaum (nee Theel). Theodor worked as a clerk, and he spent a number of years with the 79th Infantry Battalion cadets before the outbreak of the First World War.

Along with his brother Raymond Holstein Pflaum, Theodor enlisted in the Australian Imperial Force, at Keswick, South Australia, on 21 July 1915. Their older brother, Elliot Frederick Pflaum, enlisted about a month later on 24 August 1915 and was assigned to the 9th Light Horse.

Theodor and Raymond Pflaum were assigned to the 32nd Battalion and embarked aboard HMT Geelong on 18 November 1915. Shortly after arriving in Egypt for training, Theodor was transferred to the 8th Machine Gun Company.

Theodor writes of finding an injured Raymond in a dugout, as he was moving into position during the Battle of Fromelles on 19 July 1916. He writes that he gave Ray a mouthful of whisky before leaving to find a position for his gun. Raymond died of his wounds later that night.
Theodor was commissioned as a second lieutenant in early 1917 and transferred to the 25th Machine Gun Battalion. He spent some months training in England, before rejoining his unit in France in early September 1917. On 24 September 1917, Theodor Pflaum, along with four other officers, was sent with fifty men to establish machine gun positions. Whilst supervising the sending of forward material to advanced positions he was shot in the thigh, resulting in a compound fracture.

Theodor Milton Pflaum died of wounds upon arrival at the 10th casualty clearing station on 24 September 1917. He is buried in the Lijssenthoek Military Cemetery, Flanders, Belgium. His brother, Elliot Pflaum, survived the war and returned to Australia in 1919.