George McNish, Jr. was the son of an influential figure in early American Presbyterianism. The senior McNish, along with Francis Makemie and four other ministers, organized the Presbytery of Philadelphia, the first Presbyterian judicatory founded in America, in 1706. The senior McNish also helped Rev. Samuel Pumroy bring the Newtown congregation into the Presbyterian Church.

The McNish family, originally from Scotland, settled in Jamaica, Queens. Born about 1714, George McNish, Jr. married Mary Fitch in 1738 and settled into the FPCN pastorate after Pumroy's death in 1744.

After two years, McNish inherited an extensive tract of land in Walkill, Orange County, New York. He died there in 1779 after serving as minister at a church in Goshen.