Septimus, whose birth was registered at Inverell in 1888, was the seventh child of Alexander and Eliza McKenzie. He was working as a Grazier in the Bonshaw district before the First World War.
At the age of twenty seven, he enlisted in June 1915 at Liverpool NSW and became a Private with the 18th Battalion, 3rd Reinforcement. He sailed from Australia for Egypt on HMAT A54 Runic in August 1915 and by October was taken on strength at Gallipoli. By February 1916 he had been transferred to the Camel Corps. The following year he was treated in hospital in Egypt for Malaria.
Septimus returned to Australia by the Hospital transport Dorset and medically discharged in August 1919.
After the War he returned to work as a Grazier in the Bonshaw district and married a local girl in 1925. Five years later he successfully drew a 26,000 acre block in the Aramac district of Queensland and moved there. He died at Longreach in 1948.
The name of Septimus McKenzie is recorded on both the Inverell and Bonshaw Honor Rolls.