Sharpe was elected as the Member of Parliament for Ontario North in the 1908 federal election, representing the Conservative Party. He was re-elected in 1911. After the 1911 election, Prime Minister Robert Borden considered Sharpe for the position of Minister of Militia and Defence, before deciding on Sam Hughes. Sharpe later clashed with Hughes in Parliament over militia policy and the Minister's abrasive personal style. During the 1917 election, Sharpe ran for the Unionist Party. He was elected in absentia, as he was at the time serving overseas with the Canadian Expeditionary Force.
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. In November 1915, Sharpe was authorized by Hughes to raise a battalion from Ontario County. This led to the creation of the 116th Battalion, CEF, with many members drawn from the 34th Regiment and several personally recruited by Sharpe. The Battalion arrived in England in the summer of 1916 and, following training, was deployed to the front in France in February 1917. Sharpe commanded the Battalion in action, beginning with the Battle of Vimy Ridge in April 1917. Subsequent actions included an attack at Avion in preparation for the Battle of Hill 70, and the Battle of Passchendaele. Sharpe began to struggle with the impact of his military service. In October 1917, he wrote to Muriel Hutchison, the widow of Lieutenant Thomas Hutchison. 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. In his letter to Muriel, Sharpe said:
It is awful to contemplate the misery and suffering in this old world, and were I to allow myself to ponder over what I have seen and what I have suffered thro the loss of the bravest and best in the world, I would soon become absolutely incapable of 'carrying on'.
In December 1917, Sharpe returned to England for a senior officer's course. Early the next year he was awarded the Distinguished Service Order in the 1918 New Year Honours. A short time after receiving the award, he was hospitalized with a diagnosis of "general debility". In May 1918, Sharpe returned to Canada on convalescent leave. En route back to Uxbridge with his wife, he was hospitalized at Montreal'sRoyal Victoria Hospital for nervous shock.
Death and legacy
On May 25, 1918, Sharpe committed suicide, jumping from a hospital window to his death. Due to the stigma surrounding suicide and mental illness, Sharpe's history was largely forgotten in Canada for almost 100 years. 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." In 2016, a bronze plaque including the likeness of Sharpe by sculptor Tyler Briley acknowledging Sharpe's service as an MP and soldier was commissioned for installation in the Centre Block of Canada's Parliament. The plaque was unveiled in the foyer of the House of Commons on November 7, 2018.
