Post was ordained in
Washington, D.C., on June 24, 1819. He was immediately installed as the second pastor of First Presbyterian Church, Washington D.C., succeeding Rev.
John Brackenridge, D.D. John Quincy Adams was a regular worshiper there during Post's tenure. On December 6, 1824, and again on December 5, 1831, Rev. Reuben Post was named Chaplain of the United States House of Representatives. Post continued at First Presbyterian Church until June 24, 1836, when he was called to serve the Circular Church in
Charleston, South Carolina. His inaugural sermon at the Circular Church was from Acts 10:29. == Personal life ==