Tegetthoff was born in Marburg, Styria in Austrian Empire (now Maribor in Slovenia), on 23 December 1827 the son of Karl von Tegetthoff, an "Oberstleutnant" in the Austrian Army. On his mother's side he was related to Johann Kaspar Freiherr von Seiller, Mayor of Vienna from 1851 to 1861. Entering the Marinecollegium (naval academy) in Venice in 1840, Tegetthoff became a Seekadett on 23 July 1845 and witnessed the Venetian uprising in 1848/49. He received a commission upon his graduation on 16 April 1849 and took part in the blockade of Venice from May to August 1849. Tegetthoff was promoted to "Fregattenleutnant" on 16 June 1851 and "Linienschiffsleutnant" on 16 November 1852.