He studied at Heidelberg and Tübingen, and in 1820 delivered exegetical and historical lectures at Heidelberg. He received a professorship at Heidelberg from 1821 to 1829. In 1829 he went to Halle upon Saale as professor to teach church history, dogmatics and symbolics, but in 1836 he returned to a chair at Heidelberg, where he taught until 1856.  Between 1853 and 1861 he officiated as prelate, i.e. spiritual leader, of the United Evangelical Protestant State Church of Baden (German: Vereinigte Evangelisch-protestantische Landeskirche Badens).
A lifelong exponent of the "meditation school" of theology (Vermittelungs-Theologie), in 1828, with the help of Friedrich Wilhelm Carl Umbreit (1795–1860), he founded and edited the Theologische Studien and Kritiken in its interests. When Julius Wegscheider and Wilhelm Gesenius were denounced by Hengstenberg as rationalists, he pleaded for freedom in theological teaching (cf. his Theol. Bedenken, 1830). On the other hand, he vigorously attacked David Strauss. His Historisch oder mythisch? Beiträge zur Beantwortung der gegenwärtigen Lebensfrage der Theologie (1838; 2nd ed., 1866) was a reply to Strauss's Life of Jesus, and his criticism resulted in Strauss making numerous concessions in later works.
In Das Wesen des Christenthums (1845; 5th ed., 1865; English translation, 1860), Ullmann explains that Christianity is independent of the orthodox formulas, and contends that a distinction should be made between faith and dogmatics. His principal historical works are Gregor von Nazianz (1825; 3rd ed., 1867) and Die Reformatoren vor der Reformation (The Reformers before the Reformation, 2 vols., 1841; 2nd ed., 1866; Eng. trans., 1854). Another well-known work is Die Sundlösigkeit Jesu (The Sinlessness of Jesus, 1854; English translation 1858 and 1870).
- Robert Chambers , Book of Days
- One or more of the preceding sentences incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). "Ullmann, Karl". Encyclopædia Britannica. 27 (11th ed.). Cambridge University Press. pp. 566–567. This work in turn cites:
- Klaus-Gunther Wesseling (1997). "Karl Ullmann". In Bautz, Traugott. Biographisch-Bibliographisches Kirchenlexikon (BBKL) (in German). 12. Herzberg: Bautz. cols. 864–876. ISBN 3-88309-068-9.