He was educated at Brisbane, Gympie, and Laidley before joining the 1st AIF at the start of World War I.

He was stationed with the 2nd Light Horse Brigade and saw action in Gallipoli and Palestine and in April 1917 promoted to sergeant.

[1] In the same month as his promotion, Gunn was shot in the head and left elbow by opposing forces near Gaza.

[1] On 29 October 1921 Gunn married Edith Annie Curtis[1] (died 1971)[2] and together had a son and a daughter.

[1] At the 1944 Queensland state election, Gunn, for the Labor Party, won the seat of Wynnum, defeating the sitting member, Bill Dart.