John Hart was a Presbyterian.
He was identified as a Presbyterian by the Presbyterian Historical Society. (Source: Ian Dorion, "Table of the Religious Affiliations of American Founders", 1997).
From: Robert G. Ferris (editor), Signers of the Declaration: Historic Places Commemorating the Signing of the Declaration of Independence, published by the United States Department of the Interior, National Park Service: Washington, D.C. (revised edition 1975), page 72:
The year after Hart's birth in 1711 at Stonington, Conn., his parents emigrated to New Jersey and settle don a farm in the Hopewell vicinity. Hart was to live there and till the soil all his life. In 1740 he married and began raising a family of 13. In time, while gaining the sobriquet "Honest John," he acquired considerable property... He died... at the age of 69, on his Hopewell farm. He is buried in the yard of the First Baptist Church at Hopewell.
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.