Louis Sebastian Walsh (January 22, 1858 – May 12, 1924) was an American prelate of the Roman Catholic Church. He served as Bishop of Portland from 1906 until his death in 1924.
Louis Walsh was born in Salem, Massachusetts, to Patrick and Honora (née Foley) Walsh. He attended Holy Cross College in Worcester for one year before entering the Grand Seminary of Montreal in Quebec, Canada. After attending the Seminary of Saint-Sulpice in Paris, France, he furthered his studies in canon law and theology at Rome. He was ordained to the priesthood by Cardinal Raffaele Monaco La Valletta on December 23, 1882.
Following his return to Massachusetts, Walsh served as assistant pastor at St. Joseph's Church in Boston's West End. In 1884 he became professor of church history, canon law, and liturgy at St. John's Seminary in Brighton. He was named the first supervisor of Catholic schools for the Archdiocese of Boston in 1887. He was also one of the founders of the New England Catholic Historical Society and the Catholic Educational Association.