John Blair was a Presbyterian and an Episcopalian.
From: Robert G. Ferris (editor), Signers of the Constitution: Historic Places Commemorating the Signing of the Constitution, published by the United States Department of the Interior, National Park Service: Washington, D.C. (revised edition 1976), pages 145-146:
Blair, a firm supporter of independence and the Constitution, was a member of a leading Virginia family who gained more renown as a lawyer-jurist than as a politician. President Washington appointed him as one of the original justies of the U.S. Supreme Court...
Blair attended the Constitutional Convention religiously, but never spoke or served on a committee. On the other hand, he usually sided with the position of the Virgina delegation. And, in the Commonwealth ratifying convention, Blair helped win backing for the new framework of Government.
In 1789 Washington named Blair as an Associate Justice of the U.S. Supreme Court, here he helped decide many important cases. Resigning that post in 1796, he spent his remaining years in Williamsburg... He was 68 years old [when he died]. His tomb is in the graveyard of Bruton Parish Church. [The Bruton Parish Church in Williamsburg, Virginia is an Episcopal church, and is currenly in the Episcopal Diocese of Southern Virginia.]
He was identified as a Presbyterian by 1995 Information Please Almanac. The Library of Congress was cited as the source stating he was later an Episcopalian. (Source: Ian Dorion, "Table of the Religious Affiliations of American Founders", 1997).
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.