Templeton married Judith Folk in 1937, and the couple had three children: John Jr., Anne, and Christopher. Judith died in February 1951 in a motorbike accident. He remarried, to Irene Reynolds Butler in 1958; she died in 1993.
He was a lifelong member of the Presbyterian Church. He served as an elder of the First Presbyterian Church of Englewood (NJ). He was a trustee on the board of Princeton Theological Seminary, the largest Presbyterian seminary, for 42 years and served as its chair for 12 years.