John P. Knox was born in Savannah, Georgia on July 26, 1811. He got his education at Rutgers College and Seminary. From 1837 to 1841, he was pastor of the Reformed Church at Nassau, New Providence (in the Bahamas). For ten years he was a pastor of the Reformed Church on the island of St. Thomas in the West Indies.

While at St. Thomas, Knox wrote a history of the island and helped promote education. One young boy, Edward Blyden, grew up to become an ambassador for the Republic of Liberia, the first modern state in Africa. Perhaps as a tribute to teachers such as Knox, Blyden founded Moravian College (one of the earliest colleges in Africa) in Monrovia, Liberia.

Knox was installed as pastor of FPCN on March 28, 1855. During his pastorate, the Old White Church was remodeled. The old square back pews of the colonial era were replaced. Victorian stained glass replaced the small paned windows. The sanctuary lost much of its old-fashioned appearance. On his 27th anniversary as pastor, a pipe organ was installed.

Knox gave regular lectures in Newtown on his extensive travels through Europe. One Sunday evening each month, he would conduct a service and give a lecture on a religious or scriptural subject chosen in advance by members of the congregation. A monthly praise service drew large audiences. To the 109 communicants at the start of his pastorate, he added 139 during his pastorate. He died on June 2, 1882 and was buried in Sommerville, New Jersey.