Karl Viktor Müllenhoff (born September 8, 1818, in Marne, Duchy of Holstein; died February 19, 1884, in Berlin) was a German philologist and a student of Germanic antiquities.
He was born in Marne, Holstein as the second son of merchant Johann Anton Müllenhoff. In his youth, he received his education in the town of Meldorf (1830–1837). He later studied under Gregor Wilhelm Nitzsch at the University of Kiel, then continued his education at Leipzig (1839, under Gottfried Hermann and Moriz Haupt) and then in Berlin (1839-1841), where his instructors included Karl Lachmann and Wilhelm Grimm. In 1841 he received his PhD at Kiel with a dissertation on Sophocles.
He taught classes in German language, literature and mythology at the University of Kiel, where in 1854 he became a full professor of German literature and history. Afterwards, he returned to Berlin as a professor of German philology (1858-1884). In 1861 he became a member of the Gesetzlose Gesellschaft zu Berlin. Two of his well-known students in Berlin were Wilhelm Scherer and Elias von Steinmeyer.