Johann Friedrich Flatt (February 20, 1759 – November 24, 1821) was a German 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 1792 he was appointed associate professor of philosophy at the University of Tübingen, where in 1798 he became a full professor of theology.
Flatt was a disciple of theologian Gottlob Christian Storr (1746–1805), 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 an outspoken critic of Kantian philosophy.
From 1796 to 1803, he was editor of the Magazin für christliche Dogmatik und Moral (Magazine of Christian Dogmatics and Morals).