He grew up as a son of the parish priest in Tribsees and studied himself philosophy and theology at the Universities of Rostock and Greifswald, afterwards working as an auxiliary preacher in his hometown of Tribsees. In 1755 he became a pastor in Lassan, then two years later served as a minister in the town of Barth.
Spalding was an important figure of the German Enlightenment. In 1748 he released Betrachtungen über die Bestimmung des Menschen (Reflections on the Destination of Man), a publication that is considered to be a manifesto of German Enlightenment theology. In this work he rejected dogmatic authoritarianism and confessional orthodoxy, while promoting a common sense philosophy that explained an individual's path from sensuality to spirituality ultimately leading to immortality.
In his writings he was strongly opposed to Julien Offroy de La Mettrie's philosophy of French materialism. His autobiography, Lebensbeschreibung, von ihm selbst aufgesetzt, was published by his son in 1804. Other noted works by Spalding include:
Über die Nutzbarkeit des Predigtamtes und deren Beförderung, 1772.
Gedanken über den Werth der Gefühle in dem Christenthum, 1789 – Thoughts concerning the value of feelings in Christianity.