Seddon was also a veteran of World War I, where he fought in Europe and spent time in the Middle East from 1915 to 1919.

Controversially, Seddon's drill sergeant, a supporter of rival VFL club Carlton, put Seddon and Collingwood teammate Paddy Rowan through a 10-mile route march on the morning of the 1915 Grand Final.

[2] Whilst overseas, Seddon sent back a horseshoe made from a German bomb along with the remnants of a German aircraft shot down by Australian soldiers at the Battle of the Somme.

Items sent back from Seddon during the war can be seen on display at Collingwood's Holden Centre in Melbourne.

In Seddon's first season back after the war, he was a part of the 1919 Collingwood premiership team that defeated Richmond.