Johann Friedrich Flatt (February 20, 1759 – November 24, 1821) was a German Protestant theologian and philosopher born in Tübingen. His brother, Karl Christian Flatt (1772–1813), was also a theologian.
He studied philosophy and theology in Tübingen, afterwards continuing his education in Göttingen. In 1785 he became a professor of philosophy at the University of Tübingen, where in 1792 he was appointed as an associate professor of theology. In 1798 he succeeded Gottlob Christian Storr (1746–1805) as a full professor of theology at Tübingen.
He was a disciple of Gottlob Christian Storr, and like his mentor, a representative of the so-called Ältere Tübinger Schule (conservative Tübingen school of theologians) of Biblical Supranaturalism. He is remembered as a defender of Christian moral theology, and for his critical lectures in regard to Kantian philosophy.
Along with Friedrich Gottlieb Süskind, he was an editor of the "Magazin für christliche Dogmatik und Moral" (Magazine of Christian Dogmatics and Morals).