Harrison was born the son of English-born James Start Harrison in the Sydney suburb of Stanmore, New South Wales and educated at Sydney Church of England Grammar School and Bedford School in England.

[1] He was part of a Trinity crew which won the Thames Cup at Henley Royal Regatta.

He returned to Australia in 1903 and joined the militia garrison artillery in New South Wales.

[2] Harrison was promoted to major in 1914 and at the commencement of World War I was the duty staff officer at Army Headquarters and gave the instruction to fire across the bows of the SS Pfalz, the first shots fired by the British Empire during the war.

In October 1917 he joined the First Australian Imperial Force as a major and served in France at Hazebrouck, Strazeele, Flêtre and on the Somme.