Luther Martin was an Episcopalian.
From: Political Graveyard website (http://politicalgraveyard.com/bio/martin6.html#RIU0QFQ0W; viewed 7 December 2005):
Martin, Luther (1744-1826) - of Maryland. Born in New Brunswick, Middlesex County, N.J., February 9, 1744. Brother of Lenox Martin; cousin by marriage of Joseph Cresap, James Cresap and Thomas Cresap. Maryland state attorney general, 1778-1805, 1818-20; Delegate to Continental Congress from Maryland, 1784; member, U.S. Constitutional Convention, 1787. Episcopalian. Died in New York, New York County, N.Y., July 10, 1826. Interment at Trinity Churchyard, Manhattan, N.Y.
Note that numerous sources and authoritative references have been consulted in order to ascertain the religious affiliation of the American Founding Fathers. Note that the excerpts and references mentioned on this page are not the only references used in order to identify this person's religious affiliation.