A popular physician, Blanchet entered politics with his election as mayor of Notre-Dame-de-la-Victoire, now part of Lévis Quebec (then Canada East) in 1845 at the age of 25.

With the Province of Canada on military alert due to the American Civil War, Blanchet joined the militia and raised a battalion to defend the frontier against raids from the United States.

He supported Canadian Confederation as a means of defending British North America against possible attack by the United States.

In the federal House of Commons, Blanchet was appointed by John A. Macdonald to the parliamentary committee to investigate allegations related to the Pacific Scandal in 1873.

[1] The federal election law was changed in 1874 to prohibit members of Parliament (MPs) from concurrently sitting in a provincial legislature.