 Tessier was speaker for the Legislative Council from 1863 until Confederation, when he was appointed to the Senate.He was named Queen's Counsel in 1863.In 1869, his wife inherited the seigneury of Rimouski after the death of her mother; Tessier also purchased the seigneuries of Le Bic, Saint-Fabien, Saint-Simon, Saint-Mathieu, Trois-Pistoles and part of Île-d’Orléans.