Prior to the First World War, Sharpe served as a member of the 34th Ontario Regiment, joining at age sixteen and eventually achieving the rank of Major.

On the outbreak of the First World War, Sharpe was initially passed over for a command position and was not part of the First Contingent of the Canadian Expeditionary Force that deployed overseas in 1914.

Sharpe considered his past conflict with Minister Hughes as the reason he was overlooked, and expressed concern that this would affect his reputation.

This led to the creation of the 116th Battalion (Ontario County), CEF, with many members drawn from the 34th Regiment and several personally recruited by Sharpe.

Sharpe had served with Hutchison in the 34th Regiment before the war, and was present when he was injured by a shell blast, administering first aid to him.

Due to the stigma surrounding suicide and mental illness, Sharpe's history was largely forgotten in Canada for almost 100 years.

Sharpe's name was included in the Great War Memorial at the Law Society of Ontario's library in Osgoode Hall.

[1] In 2014, Member of Parliament Erin O'Toole and Senator Romeo Dallaire inaugurated the Lieutenant Colonel Sam Sharpe Veterans Mental Health breakfast to showcase veterans’ mental health issues and to recognize those "who have sought help for their operational stress injuries and are leading productive lives."