In 1781, Hardenbergh resigned his pastorates in New Jersey to accept the call to congregations at Marbletown, Rochester, and Wawarsing in Ulster County, New York. He would serve these congregations until 1785. In October 1785, Hardenbergh was called to serve as pastor to the congregation at the First Reformed Church in New Brunswick, New Jersey. He would arrive in New Brunswick to assume the pastorate in April 1786. At the same time, the trustees of Queen's College had called Hardenbergh, a devoted trustee for the school, to serve as its first appointed president. Hardenbergh was invited to fill a vacancy left by the death of the Rev. Johannes Leydt (1719–1783). For two years the church had been served by neighboring clergymen. Hardenbergh had trained both of Leydt's sons in theology—Matthew Leydt (who also died in 1783) was the first graduate of Queen's College. He would serve the congregation until his sudden death in 1790. According to church historian, Richard Holloway Steele, Hardenbergh was the last pastor at New Brunswick to preach in Dutch.
