Joseph-Octave Plessis (March 3, 1763 – December 4, 1825) was a Canadian Roman Catholic clergyman from Quebec.
He was the first archbishop of the Roman Catholic Archdiocese of Quebec after the diocese was elevated to the status of an archdiocese.Plessis cultivated a new generation of priests during the difficult period leading up to the Lower Canada Rebellion, including Jean-Baptiste-Antoine Ferland, Narcisse-Charles Fortier, Jean-Baptiste Kelly, Thomas Maguire, and Pierre-Antoine Tabeau.