Olivier Elzéar Mathieu (24 December 1853 – 26 October 1929) was a Canadian Roman Catholic priest, academic, and Archbishop of Regina.
Born in Saint-Roch (Quebec City), the son of Joseph Mathieu and Marguerite Latouche, he studied at the Quebec Seminary and received a Doctor of Theology in 1878 from Université Laval.
He was ordained a priest by Cardinal Elzéar-Alexandre Taschereau in 1878 and was appointed professor of philosophy at Laval University.
Returning to Quebec, he received a Master of Arts in 1889.
Mathieu was appointed a Companion of the Order of St Michael and St George (CMG) during the visit to Canada of TRH the Duke and Duchess of Cornwall and York (later King George V and Queen Mary) in October 1901.